I see in documentation that zorder2 is not supported for polygonal hotstpot. Maybe it is but it is not documented. In case not documented by reason that could lead to conclusion that zorder2 is realy not supported on that type of hotspots.
Workaround: Don't know if your posted polygonal hotspot is something you want to achieve or just example but in case you want to get kind of circle area you can use simple circle png image and scale it e.g. scale="25" and put it on atv="90" and you will have something similar.
Just a thought