training facility

i have upgraded my training facility to 18 level now.but at level 10 i got the same results in training players.i got 3 tp per player in 2 hard trainings and the results are exactly the same now that i`ve upgraded to level 18.how is acumulation of TP calculated?in the end maybe it`s not worthing to upgrade the training facility.
It's worth it, but keep in mind other factors that influence. Energy, age/level etc.