Yeah, you're definitely doing the right thing on disclosure!

I think some people are just going to think you're looking for a threesome no matter what you do, unfortunately, strict believers in monogamy and lesbians who are skeptical of bisexuals especially. I think it might help, though, to keep the disclosure but cut the second SO reference and the "you are female" thing at the end. (You've got filters enabled, right? There's also an "I don't want to see or be seen by straight people" setting so you shouldn't be seeing dudes anyways.) Harping on gender makes it sound a lot more like you're fishing for a third than you're just in an open relationship.

I think writing more about what you're looking for would help, talk about the sorts of F things you'd like to do with your FWB and let the "seeking hookups" speak for itself?

And it sounds like you're already doing this, but just in case: women are amazingly bad at making the first move, even lesbians. Sending lots of first messages (to folks looking for non-monogamy) is the absolute best way to up your success rate.

Good luck!

^{PS, I just reenabled my account to do this critique and a woman who kinda broke my heart two years ago just messaged asking if I'd like to get a drink and I am freaking. out.}