Yeah I think I get what you are saying (not sure how you can tell the "wasn't guided out" error -- where does that come from ?
If I have a 1" guide error then that will also be a 1" error In the imager (since we assume the scopes are moving together - assuming no flex)
Since I am 2.2 a/s in the imager, that would mean 1"/2.2 = 0.45 pixels and for my 0.76 error it would be 0.76/2.2 = 0.34 pixels
Now somehow you managed to come up with the? 1/4" "wasn't guided out" error but my RMS in the log was 0.76" total, so now I am curious about how you backed out the other approx 0.5" - is this displayed in PHD Log viewer ?