To be fair, with a rebound board, you can only hit it so hard before the ball rebounds out too far.
These boards are great for practicing everything contributing to being consistent using the 30% power.
You are hitting it over 10 times in a row, that is good. There are a lot of little things that need to be done to be able to do ten reps in a row and a lot of these translate into a repeatable offensive stroke in a rally in a real match under pressure.
Things I would exhort any player doing a drill like this is to pay attention to balance, stance, control of strike zone, bio mechanic movement, power transfer, grip pressure control, recovery.
We are seeing you get enough of these right at 30%, we would need to see how you apply these in a more dynamic situation requiring more power.
For the purposes of this kind of exercise, you are doing quite well. I might not look as good as you if it is Der_Echte doing this drill. I really suck at repetitive low power drills. Coaches in Korea groaned at my lack of ability to even the simplest FH to FH drill they love on... but when they saw I could spin the ball heavy or for power in matches, they got over their headaches quickly enough.
I say that to put the drill in perspective and not over analyze it. That drill is a building block to establish a good foundation for your base FH to be repeatable, adaptable, dynamic, powerful or less when needed.