I don't know how accurate that pic of the prechamber is, but if you look at the volume left in the cylinder at TDC, it's pretty small. The ratio of PC volume to the combustion chamber volume at TDC will tell you a lot about how the hole size will effect mixing. If the CC volume is very small, there's no point in being concerned with mixing as most of the gas is in the PC.
Also, lowering the compression ratio and substituting with boost would be ideal if you could still get it started. I wonder how much PC coating would help with starting.

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