AH HA! I had one of those moments. Much of my lack of understanding your posts and your plight came from the simple fact we define "single" differently. Where, for me, it is complete unattachment-for you it is not having a primary relationship but possibly having other attachments. Thank you for the clarification.
The comparison I was trying to make between poly singles and Vs? Hmm... Use MY definition of "single" for this analogy.
A group (three or more) of Poly-oriented singles forming a spontaneous equal relationship including them all IS TO unicorn hunting(finding a bisexual woman to fall in love with and commit to polyfi with both parties of a couple) AS....
Two poly-oriented singles forming a couple modeled relationship open to the inclusion of others from the birth of said relationship IS TO a couple finding a third who has a romantic relationship with only one member of the couple, thus forming a V.
While I know that the former are possible and do happen, the latter are a more likely scenario. Especially given how difficult it must be to find other poly-oriented singles in a community that is strongly focused on couples.
I hope that clears up what I meant a little.
I don't have any answers for you on how to feel more included. You're probably correct that many see singles as someone to invite into pre-existing relationships. To invite a single person (my definition usage) is to invite only that person and not their own attachments and entanglements as well, making it slightly easier on the couple I would think. So single polys, especially bisexual females, are sought out by couples rather than seen as someone wanting to form their own primary relationship. Or, as JR said, some couples actually want everyone to be primary and don't like having a secondary. It all depends on what each person entering or considering a relationship is comfortable with and is willing to work towards.
If you feel very strongly that you cannot be a second primary and are, therefor by default, a secondary to anyone coupled that you may become involved with, then I can't debate your feeling. If you wish to form your own primary relationship with another single poly, then I hope you get your wish. And you seem such a strong and determined woman I am sure you will and I am sure you will never sell yourself short in reaching for what you want.
Please forgive us couples though if you are so desirable we just can't resist trying.