If you don't mind sharing, may I ask how you knew/ approached these other YC Companies? Perhaps I'm naive, but I suspect a cold-email/ contact won't get me very far, especially since I'm not based in the Bay Area.
I think that if you want to be an entrepreneur, you have to get comfortable with writing cold-emails and getting lots of rejection. It's just part of the game. Plus, it's not that cold of an email: you want to do YC and the founder has done YC. You already have a shared interest.
It's tough to build credibility in a few short lines, but I appreciate the "shared interest" suggestion. I hadn't considered that this even counted. Thanks!