https://terrylove.com/wc/unifit.htm says
They recommend that the water supply be 8" to the left of center, however, for the Vespin II and the Carlyle II you can get by with 5.5" from left of center.
5-1/2" for the Vespin II, Carlyle II, Carolina II, Soiree and the Guinevere.
I expect the 8 inch number is on centers and the 5.5 is to the edge of the valve.
It appears that nothing holds your flange down, other than the glued PVC pipe. That is probably OK with the Unifit, because that uses 4 screws that you drill holes for, plus it puts significant reliance on the caulking to prevent the front from swinging left and right.
Your use of the offset flange was a good idea if you could not move the deeper piping.