Yeah, the numbers for SP reduction make no sense at all. Level 2 sucks, but levels 3, 4, and 5 are a tad better. Overall, you'll cut the SP down to half if you're level 5 - which may be something like 10-20 SP at lower levels, but scales up to 70-80 SP towards the level cap.
You can see Blaaaaaah's guide for specific percentages:
http://www.fiestafan.com/forums/showthread.php?t=3313
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