So I learned MOA/MIL from the get go on training. The math seems difficult at first but 20 years later it's second nature. Infact sold off some MIL/MIL and MOA/MOA scopes for MOA/Mildot, because I was confusing myself switching back and forth.
Bravo 4 is right the best is constants, it is eventually how your mind will lean, but I always have a dollar store mini calculator hooked-n-looped to my FMP. I also have the Mil-dot master right beside it.
Funny antidote: out field shooting the other day with a buddy who I never shot with before. He decided to "test me" by placing various gongs out there. He had the LRF but it wouldn't read the one he put waaaay out there. He tried to get the range via GPS and imagery, I trusted my math in my head that came quicker, and glad I did. Yes was second round hit but that was wind and was only 6inch off at 1150m. He was impressed.
End note: get out and try it, don't even need to shoot to practice your range estimation. Just need your scope, and somehow to confirm it.