This is especially true given how training and experience seem to shape what regions on you use (and all the more so for SJs).
Other studies have claimed a correlation between depression and preferring Fp2 over Fp1, so seems unlikely to me personally that Fp1 vs Fp2 can be entirely about type. When you look at the various things that Fp1 seems to do (deciding quickly, coming up with reasonable sounding explanations, noticing errors, filtering out distractions, and pursuing goals), neither of the IFPs really pop into mind as exemplars.
So... that's an area where I think more research would be nice since Nardi's results in this instance seem so counterintuitive (at least to me, personally).
Although, conversely, Nardi does mention F8 firing when evaluating things based beliefs of what is always good/bad. Unlike T5, F8 is about what is good and bad regardless of social context. It also seem to be a region where non-socially-contextual modesty is based.
So, anyway... don't have good answers or guesses for this, really. I certainly tend towards perfectionism myself and don't see myself as wearing rose-colored glasses. Still, I feel like I tend to define myself based more what I value and stand for, not what I demonize and stand against. It would have been helpful if Nardi had given some examples of negative F8 valuations he saw more with other types (assuming I didn't just forget that he did so).