Interesting thing to point out but a Gohan who beat someone easily who was equal to his Mystic Form was easily dwarfed by 1st form Frieza.
Which means that Final Form Frieza was well over 226 times stronger than Mystic Gohan. Who was weaker than base Goku. And even his Golden Form was weaker than Beerus according to Toriyama (and Beerus not caring/Frieza being afraid).
If his Golden Form even doubled his power, you're looking at an at least 450 times Mystic Gohan level for Beerus. Which gives some context to the amount of power he used earlier in the series or a vague level anyway.
I suspect it's less of going SSJ on top of Mystic, and more like Goku's God situation. I.E his base form retains some of the strength it had before, but he has to go SSJ to get back to his fullest.
I really doubt that Tagoma is stronger than any variation of Majin Boo, tbh.
Also, I'm not inclined to believe multipliers stay static for SSJ or otherwise anymore tbh.