Yeah, this is a long going bug in the game, since at least Arma 2, probably even Arma 1 or even OFP. I think its caused by messing with your FOV in .Arma3Profile by changing either fovTop or fovLeft and if they're not 4:3 and 3:4, map icons become squished. Here is how I have it at 1080p with
fovTop=0.75; fovLeft=1.3333334;