Basically there are two ways to run long pressure flakes.
1. If the surface has a prominent convexity, the only way I know to run flakes across the convexity and on past the high point is to keep a soft support against the rock so the flake cannot buck and break or feather out quickly. The soft pressure from leather or cloth makes the flake keep running.
2. If the surface has little or no convexity (flat or nearly flat), the direction of the pressure determines how long the flake runs. The direction of the pressure the instant the flake starts detaching is the direction that counts. As most knappers build pressure, the rock turns so that the angle of pressure at the beginning is not the same as the pressure at the instant of detachment. On flat to slightly convex surfaces, I use a slotted pad (soft pad for more convex surfaces) so the flake has an easy place to fall into.
3. Practice holding the rock while building the pressure carefully and keeping an eye on the tilt of the rock. At first it seems impossible to make that pressure point to the other edge of the rock instead of off to the side of the rock, but practice can make it happen.
WA