It's top-down, right? When you get to the part where you're concerned about fit, try it on. If it needs to be larger you should be able to just knit a few more increases. If it's too big, you can ravel a few rows and skip a few increases. Top downs are adaptable like that.
Cheating is an option. . . . Cheaters never win and winners never cheat, but smart knitters who want to retain an iota of sanity do, cheerfully. ~~Kory Stamper