So your regular 120 carrier looks like this when placed on the scanner:
View attachment 412810
and the V850 120 carrier looked like this on the scanner bed?
View attachment 412812
The calibration area is the clear rectangle that shows up at the top of the scanner bed. And in both cases, the white triangles of the carrier should line up with the white triangles on the scanner bed.
Is that how you scanned the 6x17 neg?
I scan 6x17 negs all the time using both negative carriers on a V750 scanner with no problems. I also just tried using the Digitaliza 120 film scanning mask (using the Film Area Guide) to scan 6x17 and it worked pretty well too. That arrangement looks like this:
View attachment 412813