If it won't fit, it's too big.
I have a small mouth (it's true, shut up!) so I can't open crazy wide for girthy cocks.
My honey hole can take a big boy and I actually love it when a man gives me the 4-finger wiggle to make me squirt! So that area is good to go!
And back when my backdoor was open for biz, I've had a few friends that made my mascara run when they were onboarding the island. I could handle it--but it was not at the top of my hit parade. Hence the closed for business sign.