it used to be 2% per combo point up to 10%, even though the tooltip may have stated otherwise. my googling does not exactly qualify as proof, but here's a few links about SoT not being 10%.
https://us.battle.net/forums/en/wow/topic/20749264994
https://www.mmo-champion.com/threads...ussion/page113
https://www.askmrrobot.com/wow/theor...n&version=live
I don't think this is the case anymore, though I can't confirm.