I think you have too much gear. I don't have stuff higher than the rear seat. But if I did I would lean the load to me, step forward as far as I could, and stick my foot over the seat. There is a pop up going on to the rigth with a guy jumping onto a X-cross bike, you can see his foot is almost high enough to clear the saddle. Make sure you are on the high side when mount. Another option, my wife does this all the time. She puts one foot on the near pedal, pushes off and then swings her foot over. She is 5 inches higher when she starts her mount that way. Works with horses too.
(I don't start out with stuff higher than the seat, but stuff can accumulate under the tie downs. I once pulled a groin thingie when swinging my leg up over the rear load, while on a steeply downhill section of the shoulder.)