Fuel head pressure modifiers?

Having just done the hotwire kit upgrade, and seeing
almost no improvement in fuel fade, I am thinking it
wants either a better regulator / return system, or
a better model of fuel pressure than "58PSI". I think
about a 4-5% short fuel delivery error can come from
this degree of pressure fade (stock 58 -> 52, hotwire
59 -> 54PSI).

Now I wonders to meself, whether some model of
real fuel pressure vs environmental factors, might be
buried in the code and simply not made available to
us? Certainly the plumbing losses are calculable from
fuel delivery and mechanical knowledge. But are they?

I would like to be able to bend the head pressure from
59PSI idle, to 54PSI WOT, according to data I can gather.

Or maybe I just fake the IFR table to incorporate what
I know about lower-vacuum line pressure. But I don't like
hokey.

Anybody know if it's a possibility that there exists (and
we could get at) a fuel rail pressure model?

in the new E38/67 code it exists, in the LS1 code unfortunately no.