This has been a topic before and location is "somewhere" between the transom and the rear corner casting. Drilling through the gunwhale lip will avert any major repair (other than filling holes) if you aren't satisfied with your first choice of location. Exact location is a matter of personal preference.
Here is a description from a previous post
I've also seen folks set up two straps so the skippers' back foot is in the strap about eight inches from the transom with his foreward foot on the corner casting and one closer to the rear pylon for the crews' back foot and their forward foot on the hull or tramp rail.
Don't take this as gospel, it's just my opinion.