Why did you come with this great option of Pre/Post positioning and not thinking of setting In1 and In2 level gains separately in that only case?
Actually I have the Post (In2/Out2) H9 set in an FX loop. But this loop level is preset and it clips nearly systematically In2 whereas In1 (direct guitar) tops around -20dB.
The trouble comes only for the (clipped) sound going into the H9/Post Input, as my preset loop provides a good level regarding the overall output, and the poor level that may go into In1 (but that’s not quite the problem for me).