You will probably find that the window at -20c is completely below the base level of the zone.
The -6c windows probably extend up so part of the window is above the base of the zone.
So you will either need to add a separate zone for the lower storey or lower the base level for you existing zone.
Also watch the zone height if you lower the base.
The windows need to be within the zone before they can recognise it.
One of the forum moderators.
Versions 6.5 to 25
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