Just hit level 13 on alt account. I got 40 more upgrades. So my theory of 15 upgrades per level till 9, 25/30/40/40 on levels 10/11/12/13 and then 50 from level 14 till cap seems to be the correct one. I will probably try to hit level 14/42 on alt/main account to confirm (thou the 14 on alt is more important).