I don't recall if I checked this in Divine Divinity (think it's the same), but when looking at the level dependence of experience in Beyond Divinity, I just divided the experience received for a particular creature by the experience when the character level was the same as the creature's level, to be able to check the pattern across different creatures.
Act 2 - not getting exp in BF (also included in the math appendix of the
Beyond Divinity Strategy Guide).
I didn't find the rounding of values a great inconvenience, you just need to get data points over as large a range as possible, and then double check that your best fit function matches the actual results when the calculated value is either rounded off or rounded down.
You can use
iZakaroN's SaveEditor (or from
Kiya's site, with description), if you are not already, to raise a character to a specific level and give them enough stats to survive a much higher level opponent, etc.
differences between classes (minor spoilers)
Early Starter Tips (NON-Spoiler Version) (contains much of the information in the above topic)
