That prop position in picture is at highest setting, drops another 9.5 inches at lowest setting, with four positions in between highest and lowest.
Backing plate is 1/4" aluminum sheet approx 28" wide x 19" high to spread load. (I had it rolled to match curve of transom) also passed manual bildge thruhull through center of the aluminum mounting bracket so I wouldn't have to relocate and create new additional hole.
Went with the centre location for the bracket for optimum depth during chop conditions. You can't get that low due to shape of transom when you mount to port or starboard side on a 28.
Oh and yes the entire backing plate is adhered to the Fiber glass transom as you don't want any movement towards the bow or side to side when in forward or reverse, rudder is well out of the way and steering is fine.
Beware if you want to use a Garelick 71091 with 14-15 inches of travel, it will travel that distance but the lowering distance only increases by an inch, as long as you know when you design it will help having that extra inch especially if you keep your mount off center.
(the two four stroke Garelick models appearing to have quite a difference in travel but is mainly just for lifts final resting height, with having remote control and motor locked in straight position with factory plate I chose the model without any tiller as I wouldn't want to be reaching down there as it would be obviously difficult to operate) something to think about before you decide.)