I refer to the expanded sections of the central dome as tiers. I initially discovered only two, the ‘Ray’ and the ‘Crescent’ expansion methods. These are pictured above in a manner that displays each technique. Interestingly, the bottom edge of each tier for each expansion method is identical. This means that, if desired, more than one method can be used on the same dome.
I developed the ‘Ray’ method first. Here is an animation of it. It has three tiers. From a design perspective it is unlikely that a dome would use more than three or four tiers. It would probably look too repetitious. However, more tiers would be an opportunity to use more expansion methods.
The ‘Crescent’ expansion method is the next I developed. Here is its animation. By having alternate layers curve in opposite directions the effect is more pleasing. It also has three tiers. Note: the central dome is identical to the one above.
It turns out that there is a large number of muqarnas central dome expansion methods. It is probably a mathematical problem that someone more skilled in the mathematical arts than myself could solve in a general form. However, I can point to the scope and breadth of variation with the image below.