In general our eyes are drawn to contrast. Obviously there is a lot more about a picture which can draw and lead the eye. But I feel that contrast is the strongest. Whenever I make a larger scene like this I try to think about that and where to put the contrast to keep the eye focused on what I want the viewer to focus on.
Contrast can be broken down into two things, color contrast and value contrast. So first and foremost if I feel a picture isn't working I check two things.
1. The values of the scene
2. The colors of the scene
For both those things I will want to see high contrast which will draw my eye to the focus of the picture and not to anywhere else.
1. Value check:
(Achieved by making a grey layer above the image and setting it to color in krita)
2. Color check:
(Achieved by making a grey layer above the image and setting it to Luminosity in krita)
So when looking at the values and the colors I feel like the clouds are quite a point of contrast and stand out the most. The have significant contrast both in the color check(yellow clouds with a purple sky) and in the value check(pretty light grey on a darker grey) I feel like that there is only yellow in the sky as well draws your eyes away from the knight and wizard. Also when looking at the value check I feel like there is a lack of shadows when I compared it to black and white versions of other sunset images. Also in general for light sources(sun, light bulbs, neon lights, ect.) you want the middle to be the brightest spot, where the sun here is darker in the middle than the edges.
what sticks out mst to me is the values look a bit more off than the colors in this instance.
So using the black and white version of the image and referencing black and white sunset images I modify the values:
(again messy unfortunately)
I made the brightest part of the sun the middle. I also noticed that in general sunsets had darker clouds than what your values showed. I also darkened the back of the characters to really make the back lighting from the sun pop. I also reduced the contrast in the water and in the buildings in the back ground. For the water I just uses some grey to smooth it out a bit. For the buildings I just used your darker shadow and made the shadows more prominent.
I also used the lighter sun color and put more of it behind the bottles. This helps to also pump up the contrast between the water and the bottles helping to bring the focus bad there.
Now that the values look a bit more suited for the scene. I take the original piece and switch the layer mode to color and put it a layer above the value layer.
Again it looks quite messy since there are somethings not quite suited. For example I darkened the clouds rather messily, so it didn't quite map to the colored version of the image. So that's my next step is to clean that up. However just by changing the values, I think the image still looks more cohesive and suited for the scene.
At this point though I feel the next steps are optional as I am not the best at colors, also it might have been an intentional choice for the clouds to be yellow. When looking at reference images though, clouds for sunsets were generally pink or red. Also I think reducing the yellow in the image down to the points of importance (sun, bottle, back lighting the characters). It can help promote focusing the eye there. Not to say the sky can't be the focus though.
So that's what I am doing here. I am fixing the weird shadow on the sun and reducing the yellow from the clouds down to the focal point.
Next I am still fixing the clouds but I feel some of the contrast was lost in the bottles so I pump that back up again by adding some darkness to the bottles which helps make them stand out.
Also I think that most of the back of the characters is rendered in a way which implies a more metallic material than what context would suggest. For example on the brim of the wizard's hat I think the thin bright line is more suited for metal, so I smooth it out and just gave a softer highlight there (sorry not sure how best to do this in your style).
I also saw a tangent with the shore on the left and with the knights shoulder armor. So I made that darker. Honestly if not for the tangent I probably wouldn't have removed it, though I was also unsure of it's intent since generally in a sunset I don't think you would see a highlight there. Though I didn't think it was bad.
At this point I am just trying to fix the clouds a bit more since they still don't look the best.
Lastly, I felt like the knight was more saturated than the wizard which unfairly drew attention to him when I wanted both to have equal focus, so I added more shadows to his cape which I think even things out. I also made the tip of the wizard's hat a little darker to help make it stand out(though this then makes a tangent with the horizon which isn't good, but I didn't know how to fix without moving things around more).
Finally here are the color and values checks of this final piece:
not a bit change for this first one since I didn't change much since the initial value changes.
For the color check though, I do feel like the focus is significantly easier to maintain on the knight and the wizard. As there is less contrast now in the sky compared to their highlights, the sun and the bottles.
I don't think this is the exact end product you were going for, but hopefully this gives you some ideas on how to make something more true to your own vision. I would recommend making a thumbnail with the composition, colors and values for the scene that you want. I am not sure how easy it is to change these things on the fly with your art style, so it might be easier to make a messier smaller version which is less commitment and easier to try and get the right feel and then transition to rendering the final full piece. Usually if it looks good and clear at 1/10th of the size, it will look better when scaled up as well.
