Since you said the same thing happens with the BTR3 connected to the P20 my guess is that something about the EMUI is limiting the “bass boost” you are using.
In any case EQing the BTR3 directly from the fiio app would be a solution since you have direct control over all the frequencies and the EMUI cant do anything about that (since the changes are local in the BTR3 memory)
Tried it, but it doesnt really help. I dont have any local files, I only listen through spotify.
Also coming back to the Pocophone, connecting directly and plus bassboost its a nearly perfect sound.
Using the BTR3 with the Pocophone and the exact same settings: nearly half the bass.
This is sad. Might try the earsonic ES100, atleast that one got a global EQ thrhough the app