1) Take your feeler gauges apart.
2) Pair up a size that can be duplicated with one of the remaining feelers.
3) Take the thickest 2 feelers gauges, clamp them over operation No. 2, but, have both of them overhang by10mm.
4) Slide the feeler gauge that you want to "get the feel for" into this gap.
there, now you know how it should feel.
If you have more than one set, you can put the correct feeler gauge in the sandwhich in the first place without faffing about making the gap up.
If you have a vernier or micrometer, you could set this to the size of the feeler you need to get the feel for.
What I did years ago, when I had a bike with difficult access, was to close all the gap, then wind the adjusment out 90 degrees. This was because I knew the pitch of the threads, just convert this to an angular rotation.
So anyone know the pitch of the screw on the GS?
I've not done it this way myself though
As another pointer for the "feel" for it, I'd also say that the correct gap should just be able to slide in and out with minimal resistance, wheras an oversize feeler gauge would have to be forced in. an undersize gap by comparison would be obviously a sloppy fit. I.e. you would check what is perceived as being the correct fit, by using the next size up and down as Go, and No-Go gauges.
(Not the correct engineering terminology in case anyone has a pop at me, A) Go correct size. B) No-Go Oversize. The Go in this instance should fit, but the N0-Go should not.
Engineering lesson over.