"The first thing I do at the start of every interview conversation is ask comp. I then tell them my total comp and ask for X% over."
First, no good team will hire someone that does this, second, this is not a good negotiation tactic at all.
On the former: definitely it's prudent for both sides to be 'in range' or else it's all pointless, but that should be sorted out before the interview process - just the range.
Anyone wanting to talk about salaries up front is not going to make it past that part of the conversation for any decent group. It's the last part, not the first part, for so many reasons not the least of which is trying to put a number on something wherein fit, value etc. has not been established, and more obviously a concern over motivations etc..
As for the later, i.e. 'why it's a bad negotiating tactic' ... because it's not just about Supply, it's about Demand as well.
You may be overstating or understating your position by quite a lot thereby rending moot a real opportunity for exchange of value.
You may have some kind of special skills they really need, and some advanced insight. They might also be in a very profitable position. They might be happy to pay you much more. Alternatively, you may have little to offer, they might be cash constrained etc..
For equity again, they might be offering you a sweet deal, above industry norms, in which case asking for 2-4x just seems aggressive or uninformed.
But really, both of those things combined are bad: anyone wanting to talk comp details before demonstrating value, commitment, professionalism and the incidentals like curiosity/intelligence ... as an employee that's 'really bad signal'. If you're hiring someone you know to be a competent contractor, the scope of the job is established - fine - but that's rarely the case.
YC doesn't publish comp because it's probably not very helpful, the range would have to be wide, and they probably want people who want to be there, the comp distracts a bit from that. That said, I wonder if there were a sea change on that custom if would all be better off.