As far as I remember, if training 1 position is a unit of training received, 2 positions are 1/2 and three positions are 1/3, at which point it's quite easy to do the math;. But don't quote me on that, since I can't remember for the life of me where I picked this piece of info.
I hope it isn`t that way, because there wouldn't be any reason to train more than one spot then. With one spot, your players would improve much faster and you would get as much overall training as with two spot training.
This is a strategy game, and you are supposed to make strategic choices. There is an strategic choice if a player with 2-spot training gets less training than a player in 1-spot training BUT you get more overall training with a 2-spot training
(the same could be said for 3-spot training and team training)