[Les]

Maybe some of limitations are using "C/W"or "W/C" values obtained at set Tai and Twi for operation at other Tai and Twi
Am crudely exploring these limitations using my old friend Kryotherm(must be good, it is Russian)
Possibly the most common situation is Tai is "comfort controlled at 25c(say)" and Twi varies.

Initial play suggests only a small influence on Rwetside for a 120x120x30
Possibly 1% for change from Twi-Tai=5 to Twi-Tai=25 for Rad with C/W=0.06

If anyone is interested may post any further numbers, if not will not.(if continue ferreting)