Since patch 1.18, levequests were changed so that most of the SP gain was moved from the mobs to the reward you get at the end of the quest, in order to solve the whole "levequest link and drop (rinse and repeat edition)" issue. So for "Desert Defilement", if I remember well that's 5 Peistes, who give you 220 per mob, but you get around 5k at the end so that's around 1200 sp per mob. Please also note that most side quest mobs also give less SP, so that people don't go grind and decimate the mobs that are needed for someone's quests ^^"

Moreover, since people where complaining that lower levels took way to much time to level, a "exp" multiplier is applied to the base exp you should receive for the mob. It starts from exp and SP x 4 at rank 1 and decreases to drop to 1 when you reach 24.

Hence the differences in SP figures you've been noticing. I hope this was helpful.