Could you try the new Version 1.26? To see if solves that problem?
Unfortunately no, don't have 1080ti nearby now.
I can confirm the increase if 0.1Mhs in my Ampere... and I 0.15 Mhs in 1070ti and 1660Super.
For 1070 and 1080 I have to put the --mode a to get the extra Mhs.