I think I found the problem : the stat you've collected from the game are used ingame as a basis for the level 0, while you use them starting as level 1. It would explain while selecting the level 20 in the talent calc shows the same value as the game has for level 19

I needed today to check multiples heroes base stats at level 20, like hp, regen, damage, ... It seems they weren't refreshed since a while, or the formulae behind is off : Level 20 heroes, ingame training mode vs HF talent calc - IG tracer : 2807 hp, 11.63 regen, 57.0 dmg talent calc : 2697 hp, 11.23 regen, 54.78 dmg - IG Kael'thas : 3334 hp, 6.88 regen, 142.5 dmg talent calc : 3202 hp, 6.67 Regen, 136.95 dmg - IG Illidan 3619 hp, regen 7.50, 171 dmg talent calc : 3476 hp,...