Hello,
When a pie chart works in SpiderNoOverlap mode it fits all the labels within the bounds of the pie chart panel. If there is not enough room to fit the labels, the pie is getting smaller in order to free some space.
It is important that the labels don't go outside of the panel bounds, because this allows for layouts with many panels where the pie labels do not overlap the contents of their neighbor panels.
The other pie label modes (center, rim, spider) do not manipulate the size of the pie, so if you need equal pie sizes you can use one of these mode. However these modes do not check for label overlaps and allow the labels to go outside the panel bounds.
Best Regards,
Nevron Support Team