I think, the reason is that you place the input ac voltage source on no-invert input of opamp to get phase decrease from 0.
you can get phase decrease from 180/-180 if you place the input ac voltage source on invert input of opamp.
Added after 8 minutes:
Sorry, what I say is for the case that ac source is placed input of opamp.
The question what you say maybe the same reason. It is only because ac source direction.
I suggest you release in analog ic design board. There are many experienced people who work in analog area.