This is exactly what I do. For reference we are about the same size. I'm using an XL Mantis and while i like climbing on the stock bridge, I do get some hip pinch after a while using it. I just swap in my lineman's belt and adjust it to about 35-36 inches. I also wear the Mantis pretty low, waist band just above my tailbone. I am a sitter (knees to the tree) and I find this works very well for me. As others have said, playing with different saddle positions, tether heights and bridge lengths cna make a world of difference, and it doesn't always seem to take a big adjustment to find the sweet spot.
It does seem though that different manufacturer's saddles fit people differently. I know its late in the season but an option down the road might be to sell the Mantis and look at the Aerohunter Kite. These saddles are holding their value pretty well.