We probably duplicated some work here, LOL. I did something similar for the Land, Sea and WorldMap and if you want to try the files, they are here: https://mega.nz/file/j1EXzYhC#l_msNecCG42iah5cHdLK5wDIEBauMoxbu2w8CuUwY-M
However, given you were not satisfied with 1080, my version will still be too small, but I centralized the number for the ratio calculation, so it only needs to be changed in one spot.
Near the top of the BattleInterface.c file:
#define BI_COMPARE_HEIGHT 1080.0
Change that number to maybe 800.0 or 900.0? Let me know which number you think looks better and I will probably just use your preference in the upcoming update. Later, I will add an option to allow adjustment on the options screen.