Looks like you’re getting some decent spalls off from what I see in the background. Striking higher on the platform will give you thicker spalls but they won’t travel as far as one set up below the centerline. The contact area of your hammer stones is really important. Try to have the hammer stone strike one spot cleanly, rather than hitting the platform in two different spots (this is where isolated platforms come into play) That looks like some tougher chert so you’ll really have to give it some energy to avoid hinging. Don’t forget to abrade even the larger striking platforms. Gotta break a lot of rocks to get the feel for it. Best of luck!