the way i look at it is like in an rpg, at level one you need 10 points per training point, at level two you need 15, at level 3 you need 20, etc , with an initial training giving four points, so 3 trainings give you 1 training point at level one, four are needed at level 2, and 5 at 3, each time you upgrade your training grounds they give 1 more point, so after one upgrade you now get a training point after 2 trainings at level 1, 3 trainings at 2 and 4 at level 3
Note: i don't know the exact figures, these were for explanation purposes only