Have just purchased a seat harness after having used a waist harness previously.
Decided to give the seat harness as i think i can get more mast foot pressure with it.The seat harness seems to ride up to my chest when i try to exert downforce (probably my expanding waist is the problem here.

Anyone got any tips on differences on set up between the two. Have got 26'' lines at present but going to stick on adjustables with the seat.

I've always been a seat harness user so can't really make comparisons. I can't picture how the seat harness can ride up to your chest, easy to see how a waist harness could, especially if your butt is getting a little wide. With the seat harness isn't it just a matter of tightening all the leg and bar straps so it simply cannot move. Most I get is a slight wedgey in extremely string conditions.

I use 28 lines on my freestyle board and 30+ adjustables for my formula.