i used to get complaints about my drum monitors, which were small and not loud, but by using my computer’s monitors, which are far out into the room, Genelec 8020’s I think, I have not gotten complaints.
If the neighbor is really cooperative and motivated, you could speak on the phone while moving the speakers around to see if one position is helpful.
I used to have tenants living next door with a small system and subwoofer- it really excited the wall between us, but playing my full band with system and going next door I didn’t hear it. I think some cheap small subs or speakers use a resonant frequency to simulate full sounding bass, and that can be problematic.