There's vulvas where you can directly contact the clit, and others where you have to separate 1 or sometimes 2 sets of lips to expose it. It's completely different (or at least additional) actions required. Licking a 2 inch longer dick doesn't seem much different, nor does a thicker one, in what you have to actually do.

I agree the dick differences would alter the user experience a lot, but not in a way that makes it more difficult.

But I admit I'm possibly biased as a dick haver and not a dick sucker. We need some bi peoples' input here lol