cart height

It will make a difference, but how significant is hard to predict. If your arm allows for height adjustment to set the VTA, try lowering the arm to reduce sibilance.

Sibilance can be based on that but normally it is wrong alignment or mismatch cartridge and arm.

The cart is a Soundsmith retipped Denon DL-S1, alignment with a Mint protractor on a Audiomods Classic arm. I tried 1.15 to 1.5g VTF as well.

Depends on what angle your stylus is mounted on the cantilever compared to your last cart. The angle can vary even with the same brand/ model. As suggested above try lowering the back of the arm to reduce sibilance. Also you may need to try a different loading of this cartridge than the last one you used. Try lowering (numerically) the loading to see if that helps.

I tried a few VTA settings to no avail. So I decided to recheck my alignment, and take my time. You see, I can can set up a Denon DL301mk2 - Dyna 10x5 and a few others lickity split! But I found out how critical a severe stylus shape can be to align. Close is not good enough! The sibilance is now gone.
Cheers, Doug