Sometimes only a stirrup will do. I've spent hours hanging in a simulator tweaking settings, but it seems some harnesses just don't suit my 6'3" frame. Clothing does seem to make a difference - jeans are better than my flying suit. For paragliding my reversible harness and pod harness are fine, but my seatboard harness and tandem pilots harness (which are most similar to a paramotor harness) won't work whatever I do, and a stirrup is the only answer (or pushing my knees into the poor passenger if flying tandem!).
I couldn't agree more with the comments about keeping the brakes in your hands whilst reaching down to push the seat forward - I've seen someone stall and pile in doing this on a thermic day, and i've seen some pretty close calls with people flinging themselves wildly around as they try to get into the seat - hard to maintain control of the throttle doing that, and a glider wobbling around aand barely under control close to the ground is asking for trouble.