UPDATE: I fixed a bug in copying your data 
Hey, thanks for the data!

I quickly put the data you posted into a chart to get *definite* upper and lower bounds for the mana pool per spell, and get definite overall bounds (instead of the approximation by the middle value).
Assuming that the power pool percentage displayed is actually ROUNDED (up or down), the result looks like this:
This means that you power pool is between 318 and 320. The more spells you add to the chart (preferrably with high power consumption), the more likely you will be to tighten the boundaries.
Assuming that the displayed percentage is ROUNDED DOWN (always) e.g. a remaining power pool of 91% after one cast means that the spell costs anything between 8% and 9% power, the chart looks like this:
Meaning your powerpool is anywhere between 350 and 350

Note: I assume that you did always wait until your power is back up to 100% before casting the next spell. Otherwise, rounding errors might accumulate.
The best way to find out whether they are rounded down or rounded symmetrically is to quickly do multiple casts of one of the expensive spells, e.g. the one that costs 30 or 28 power, and add the overall result to the table. It might be necessary to repeat the test in case you get unlucky and the power is "ticking" in between the casts. At some point, one assumption (rounded or rounded down) will get contradicting while the other will not
