I tried a piece of blue chalk. No real difference.
Any ideas about my other question, why my impact point is still well above where I'm aiming on the CB?
Look at your original pictures. The position and angle of your right hand in the picture "stroke just before impact" is where they should be "at impact". I think that's what I'm seeing in the pictures but due to angle, etc it could be deceiving.
I would try moving your right hand (while keeping your bridge hand stationary) back about 2 inches. Change nothing but that. Do this when your tip is right at the CB. The relationship of the tip to the CB should not change. If it does then you moved something else in addition to your right hand. It will feel uncomfortable, try it anyway.
Now do everything you've been doing (practice strokes, etc) exactly the same as before. Do this while shooting a shot, maybe a fairly easy 2-3 foot shot, medium speed, intending to draw back say 3 feet.
I said the same as usual but you might want to change a few things. Think about and/or do these things before getting down to shoot. Use a regular CB. Whatever your grip pressure is, lighten it even more. Increase the speed about 25 percent. Forget (completely) about your elbow.
When down ready to shoot if you have to think about anything other than "nothing" then the thought should be "smooth".
Oh, almost forgot, chalk up.
Might work, or not. Best thing would be to go to the poolroom, ask who the best player is then ask them if they'd be amenable to you asking a few questions over drinks which you'll be buying. Just don't be buying Billy Thorpe any drinks please.