Yes they say for every 12" back you go up 1" so a 30" set back will go the 3 inches.
But that said I did not like how high up on the V20 transom it had to go!!
So I just mounted it like a 25" shaft should be with the cavation plate even with the bottom.
I have not had any problems at all!! and the motor stays out of the water just fine.
The decision will be yours at the time. Look to see were the bracket is on the transom when you do it and decide for yourself.
Thats why they call it a coustom fit! ;) *But you have to be at least 25'!!
Make sure that you measure from were the motor mounts on bracket!!
Comon mistake i heard about is some people forget about the 3" lip for the motor when they drill :o
