Bump for this...I am still on Project Fi, but using an original Sprint build. My wife has said my phone sucks since getting Project Fi and it goes to voicemail a lot now. I noticed that the handover isn't so great if I am in a bad area, typically when I see an H appear next to my signal it sucks the worst.
I wonder if flashing a Project Fi specific factory image would resolve this? I am thinking of doing that, or waiting til marshmallow comes out and hope they perhaps come out with one unified build.