So, your flakes won't travel all the way across, beautifully, until you remove those ridges. The energy wave can't travel through the ridgeline. Your strikes are moving directly into the ridge, which is why it stops there and you are left with a step. Bear with me...picture yourself going hiking and imagine as if the piece of stone's surface were the ridgelines you were going hiking up. You wouldn't want to walk up the steepest incline. You would want to walk along the gradual rise of the topography. Does that make sense?
Look at your piece of stone starting out primarily from the centerline, first. That is, look at it from a thickness perspective instead of the side profile. Considering both sides, you want to remove the thickest portions first, preparing a platform on the opposite side of what you intend to remove. This is where "centerline" comes to play. Take a sharpie pen and actually draw the centerline around the circumference of the stone. Everything to the right must go right. Everything to the left must go left. You are creating platforms to strike so that you are climbing the ridgeline in the direction of the gradual rise of the topography.
Considering your photo, here is my 2 cents:
Remove the Red 1 portion first in the opposite direction of the showing face with respect to centerline. This must be done to have a clean platform to strike in the direction of 2 and 3 respectively to thin the piece.
Abrade, abrade, abrade. Think about abrading with a great deal of pressure vs. very lightly and what difference that makes.
How tightly you hold the spall with your left hand matters as much as the proper placement of your strike with your right hand. Squeezing it too tightly will dampen the energy shock wave travelling through the stone.
When using percussion...think about "follow through", like with other sports. Follow through your strike.
Hope this helps.
Parnell
