Put the hush right after the guitar this is where it will be the most effective. The idea is to cut the noise at the source. To put it in a loop will just frustrate you, when you change a channel it will react very different with the Hush, it would most likely gate your r1 too much and not enough for R3. (Depends how you set up your amp but you see what I’m getting at).
I recommend for setting it up, kick on your direst channel (leave hush off for now) go to the nosiest pickup select on your guitar (gonna be a little noise for now) then turn the volume down all the way on the guitar, Kinda make a mental note of the ambient noise that’s left coming out the speakers. Next kick the guitar volume back up aaahhh lots of noise again, engage the hush. And start tweaking till you basically get the same ambient hiss that you had when you had the guitar volume all the way down.
This should put you in the ballpark very quickly you will still find yourself tweaking a bit.