10% of SSJB

[SSJ2]

I assumed that they became more effective at maintaining Blue's power after that. Vegeta did spend time in the RoSaT specifically training to minimize Blue's strain in Bursts, so I highly doubt the stamina loss was that bad after that point. It still seemed significant for Goku who was extremely exhausted from using the Mafuba.

 

[GreatSaiyaman123]

I like SSJ2’s explanation that sealing the aura means accumulating power beyond SSJB level. It’s like how an amplified blast raises your PL, even though you’re just gathering your Ki on a certain point. Only here the “certain point” is your entire body.