If I’m understanding you correctly, no you do not need this thoughtform for your evocations to work. I remember you sharing a sigil from one of Corwin Hargrove’s books. That author has good methods so if you use them the magick will work and you will connect with the appropriate spirit.
People really freak themselves out about imposter spirits. I’ve never had any problems with this.
There was this one time when a demon I had summoned pretended to be a different demon and tried to spook me. I banished it and that was that. That was the demon giving me an experience to relieve these sorts of concerns.
I don’t mean to discourage people from asking questions, but it kinda seems like you’ve been freaking yourself out a lot for no reason. Just do some magick and chill out my dude. Maybe do a ritual to help you chill. Not every ritual has to be earth-shatteringly sublime with exploding energies and all that stuff that happens sometimes.