For the longest time I just followed the "1-2mm" advice for how much clearance there should be between the piston and squish band. But really you want to size that gap so that the gasses are exiting it at a max of 15-20 m/s. With the spreadsheet I can adjust the gap till the velocity is where I want it. It also gives me the compression ratio and a few other important bits. There are a few more things I'd like to add, like allowing for an offset of the bore axis to the crank but that is seen more in 4T engines.
Squish velocity as a function of crank angle at 7000 rpm
MotoBi cylinder head, the motivation for finishing the spreadsheet.