Screen size vs. 2nd anode voltage

[zenith2134]

Hey I was poking around in one of my old sets and got to thinking. What correlation did crt screen size have on the high voltage at the 2nd anode? Digging through some Sams photofacts, I see 13" color sets from the seventies with anode voltages up around 18kV while some 19" color sets in the eighties were about the same....
I realize that HV regulation is a huge part of the performance of the set during its life, and maybe higher=more stable, but I don't really know. I notice a lot of Trinitrons from the eighties seemed to have higher HV. Thought this'd be a cool thread. anyone?