Dear Martin,
I encountered a similar issue.
However, after some digging, I found an answer buried in this discussion linked below.
Basically, the small “strategy percent of time” is intended.
Quoting Chris Mackey:
"Not all hours that fall within the passive solar polygon are counted as comfortable and a given hour is only considered comfortable if it falls within the polygon AND the solar radiation for the last few hours of the EPW is enough to overcome the temperature delta between the outdoors and the building balance point. "
The thermal mass+night vent behaves in a similar way too:
“The thermal mass+night vent is using a similar method to the PSH polygon in that it will only count a given hour as comfortable if there were cool enough temperatures in the previous hours to “night flush.” For this reason, even though the thermal mass polygon looks large, there are often a lot of hours inside of it that are not comfortable because the preceding hours are not cool enough.”
Hope this helps!