is from the official Aries
It is difficult to be precise, but it seems rather more than 3 inches off center.
The site has been redesigned since I last visited it (some years ago) I was sure there used to be something about off-center mounting being acceptable.
Obviously, the boat will behave differently on a different tack, a combination of less servo pendulum in the water
on one tack, and maybe a different airflow over the vane. However, 3 inches doesn't sound a great deal. It equates to 1.4 inches higher or lower than centerline mounting when heeled at 25°.
I think centerline mounting is best, but if you need to go 3 inches off, then it is no big deal (IMHO)