Flaws in this include assuming that UHI is confined to the boundary layer on a calm day, assuming that we only care about heating of gas molecules, and the portrayal of UHI as a sort of «bulk» ground effect.
Oncalmdays, I expect both the UHI effect and the NSTI to be operating in full force: whatever heating is provided by the urbanization will be operating without being blown away; and whatever cooling is provided by the NSTI will also be protected by the stratification of the boundary layer.