Please clarify exactly what information is needed for a proper HIR-FT curve.

Within the boiler property dialog box in Water-Side HVAC, the performance curve for HIR-FT shows f(t water entering, t water leaving) and while hoovering the moose over the input box the comment "Bi-Quadratic Curve: the HIR-FT as a function of the temp of entering and exiting water (undefined)". Yet a click further to the item help page states "...as a function of the supply temperature and the environmental temperature. "

While I have completed a curve based on entering and exiting water temp and have seen expectable results using it, it has been said that this is inaccurate and the curve should reflect what is shown on the item help page. If this is correct please detail the inputs needed to complete the HIR-FT curve. With no sight in mind, I would say the supply temp is 180F and the environment temperature is slightly above the building air conditioning setpoint temp at 75F-80F and these numbers will be fairly constant which would not really yield a curve.

Thank you.
Kevin