Experience Point Weirdness: Is my math funny or theirs?

[mneme]

Monster experience is sort of funky because they decided they wanted experience to be the basis for mix-and-match encounters. So monster experience is linked to relative challenge.
...
So there are a few cases where character power goes up dramatically... level 11 and 21, most notably. These influence monster relative challenge for the levels near them.

This.

Monsters of level 11-20 are more powerful/level than monsters of 1-10, and monsters of 21-30 are another bump. This is clear given that PCs get a similar bump going from 10th to 11th level, as they get a whole new set of class features added in to their original ones.

So since experience determines how much of an encounter's "value" a given monster is, monsters past the post are worth more experience to reflect their greater challenge. Since 11th-20th level monsters are worth more, 10xtheir exp is bigger.

This does mean that near the jumps, level+3 encounters get much harder, then again, this is reflected in the relative xp values.