Different tab types,require different mounting and placement methods.
I just finished installing a set of Bennett 12"x12" drop fin tabs.I actually spoke to the folks at Bennett while i installed them.
My tabs required they be mounted with the leading edge flush with the hull bottom,and the trailing(outer) edge,at a negative 5/8".
Other Bennett tabs,like the sport tabs, call for the leading edge to be 1/4"above the hull bottom.
They are pretty easy to install,if you take your time and follow the directions.
They recommend mounting all their tabs as far outboard as possible(about 3"in from the chine).
Here's a couple pictures, of the tabs on my transom in progress.
