Shaun, did the rim show first? it looks very similar to what I experience, though I think my center baldness might be slightly more pronounced. Do you also have about 1 mm between rim and tamp at every edge? I know there are different 21g baskets.
You know, it really depends on how careful I am with my distribution and all the other factors. I must also mention that I know it should be the same for every bean but some beans or blends are a bit more resistive to a perfect "complete screen fill" and can be a bit splotchy at times. Sometimes I will get rim show first, today was an example where I was pulling Daterra Monte Cristo, yesterday didn't have rim show first and I was pulling Harrar Bagersh. Granted, today was a bit of a rushed technique as it was a late-day shot and wasn't as precise as I should have been.
I do have approx 1mm at the edge and I'm using a Reg Barber. I've tried a pile of different techniques to defeat the rim show, something that might help you is as follows:
Do your distribution as you typically would, WDT or whatver, when you get to the finger distribution (whether you use Stockfleth's or modified-whatever) create a smallish crater in the center with the circumference built-up just a bit more. This is a subtle elevation difference but will only be understood with practice. Then I use either a NSWE tamp or a nutating (rotating around a center point so the edge gets a seal) motion followed by a straight down tamp at 30lbs. All of this is dependent on my mood at the time and how I feel the bean needs to be pulled.
Let me know how you make out with it.
