You don't use a radius block to make a fretboard.
Well, I guess you could, but that sounds incredibly tedius and probably takes forever.
Radius blocks are for finishing, finalizing the radius.
Your best bet is to draw the radius on both ends of the board, and use a plane to roughly shape the radius. From there, use a LEVELING BEAM with 80 grit sandpaper to finalize the radius. This will ensure consistency, and the method caries over if you ever want to make a compound radius board.
After that, use the radius block to smooth everything out and put the finishing touches on it.
Lately, I've been using the router table to radius fretboards. I use doublestick tape to attach the board to a chonking piece of angle iron, run it through, flip it over, run it through again, then onto finishing with the beam and block. Here's one of the bits. If you don't already have a router table it may be cost prohibitive. https://www.amazon.com/SJE-Tools-Fretboard-Router-Radiusing/dp/B08G18B9RH/ref=sr_1_6?dchild=1&keywords=fretboard+router+bit&qid=1617388120&sr=8-6