If it were mine I would lower it down until the bottom of the cushion on the trunk was sitting right on top of the seat just like in the picture of the wing. Thats how my wing is.
If you have a lower luggage rack that is made for the 750 you could mount the trunk on that.
As far as getting on the bike instead of swinging my leg over the top I bend my leg at the knee and slide my foot over the passenger seat. It was a little awkward at first but now it's automatic.
Peter