If you’re going to pick apart 8 year old posts, then you have to read them fully.
The OP states- “The check engine light comes on, usually when the gas tank is just above half.”
In this condition, the EVAP monitor DOES run. If the gas cap was loose, then you would also trigger a gross EVAP leak diagnostic code. Same if the purge valve was stuck open allowing un-metered air into the intake. In the absence of those additional codes, I stick with my original assertion.
I’m familiar with a few manufacturer’s systems for EVAP monitors. None of those had any qualification on ambient temp. Only tank fill level. In fact, I once had to resort to exploiting those conditions to pass emissions on a Camry that had a pesky intermittent small EVAP leak where the gas cap sealing flange had rusted and I didn’t want to exchange the fill tube in the dead of winter. The cold didn’t stop the EVAP monitor from triggering CEL. Which ones use ambient temp as a qualifier?