I'm getting ready to try my hand at an image with a gradient - just one color. My basic understanding is print @ 22.5 and 45lpi. I also understand that I'll experience "dot" gain of 30-40% when I print but what shape should the dot be? My RIP software gives me these options - is there a standard or does it "depend"

:
Round
Diamond
Line
Elipse
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An additional question is, is there a formula for determining mesh size for the printing. This image will be 8"x4" - black plastisol on white T - for testing purposes I was going to burn it on a 230 screen but at this point it's just a guessing game for mesh size - I don't like guessing
The image will be similar to this but I still need to lighten gradient to account for dot gain. Thanks in advance!
