I started training this type of player last year and have always had a lv 4 trainer. Other than two weeks during which I trained him in Jump Shot along with my other big guys, I two position trained in IS/ID/REB for the entire season (once in BLK) and he popped every single week (as an 18 year old). I think the height differential nearly makes up for difference of 1 pos training vs 2 pos training.
As a 19 year old this season, he did experience his first non-pop training although it was partially due to the fact that I trained him in the big guy stat that he was already the most skilled at and I know that slows training down some.