Oh, I posted it in the bar sport because it was so far off subject.
It also misses the target voltage by a half volt or so when in circuit on a battery.
A bunch more testing in circuit led me to look at the regulator. I'm not totally sure about this, but it appears that the 'good' regulation of a 7805 isn't as good as I thought it was. With a supply a couple of volts higher than the regulator I get about a half volt deviation between no load and an amp of load.