[click these to see closeup]
I just eyeballed it, was careful, and got into a 40 LED rhythmic human production cycle. I stopped grinding when the dome part was completely gone, just straight cylendar sides left. I preferred to leave part of the dome than remove too much, so sometimes there's a very slight curve on the LED sides, but it's not noticable.
So they're all unique, organic... like snowflakes.
So the only thing you can notice "wrong" is that a few of them seem a little lower or higher than others (I'm talking very small nitpicky amounts), but I think the tolerances for error in my results are near pro gear, looking around at some other synths.
The battle was to hold the LED straight so the flattop was level against the grinding wheel.
A jig piece of wood with a hold drilled into it might make this process easier. Please post if you do something like this.