Unless you have some kind of very unique skill or you have other offers and the company really, really wants you, how exactly are you supposed to negotiate?
Every comp negotiation I've ever had with a company has gone kind of like this:
[Company]: Here's your offer for $X.
[Me]: I'd like $Y.
[Company]: Your offer is for $X.
[Me]: Well, I think I bring skill A, B, and C to the table, and here is some data showing someone with my experience tends to make $Y.
[Company]: We don't care. Your offer is for $X. Are you interested or not?
[Me]: How about vacation time or benefits? Or maybe salary vs. equity? Can these be adjusted?
[Company]: <yawn> if you don't want $X, there's the door. We have 35 other candidates in the hiring pipeline.
What magical incantations are you guys speaking that allow you to make any progress against these brick walls? I've never once, in my 25 year career history, ever gotten a company to offer more than their initial offer.