I've had the same problem with mesh bed compensation and tapering.
Tool offsets were around 6.5mm for T0 and T1 and 3mm for T2 and T3
With M376 H5 (taper off until 5mm) I barely noticed any z adjustments on T2 and T3 and absolutely none on the first two tools.
To confirm, I tried M376 H15 and can see z moving cleanly on all tools.
As it seems, tools offsets is not a part of the calculation behind M376
Hardware: Duet3 MB6HC + 2x Duet 3 EXP3HC
Firmware: MB RRF3.1.1 + EXP RRF3.1.0