Increase the size of the background image
I'm refering to the small background image that loops from one side of the map area to the other. It seems very small and barely works as a background image. Back in Worms 2 it was alot taller.
If WA uses the exact same image file as W2 then it should be easy to just raise its height and reveal that bottom half of the image?
I just went and checked, and the bottom of the Sports background image aligns very closely to the lowest point you can see in the water. I don't think it could be raised by more than 5-10 pixels. Looking at the screenshots you posted, there doesn't seem to be a considerable difference - remember that there are two more water lines behind land in the W2 screenshot which are not visible. The screenshots are also at a different resolution.
The small background image at the bottom which can be removed by taking down the background detail. With the ingame colour maps this image is of white mountains.
I always rememberd it being bigger in W2 and today decided to look it up. In W2 that background image is definetly taller as you can see detail on it that's not visable in WA. Check gamespot, they have a screen shot on both W2 and WA of the sports theme, so you can conpair easily. In W2, this background image is also lighter but I guess that was done to give a wider contrast with the terrain.
Worms 2: http://uk.gamespot.com/pc/strategy/worms2/images/0/1/?full_size=1
Worms Armageddon: http://uk.gamespot.com/pc/strategy/wormsarmaggedon/images/0/3/?full_size=1
Could you please clarify if you mean the dithered background gradient, or the background images at the bottom? Are you sure it's really smaller than in W2, and it not being a matter that W:A supports higher resolutions than W2?