from Main FAQ
Do spell resistance, damage reduction, or caster level
for spell-like abilities increase as a monster advances by Hit
Dice?
Unless a monster’s description states otherwise, most
monster special abilities aren’t Hit Dice-based, and thus are
unaffected by advancement either by HD or by class level. (An
exception is the save DC for any monster special ability, which
is specifically described as using HD in its calculation).
Again, a DM can create exceptions to this rule; for
example, increasing spell resistance by +1 per point of
Challenge Rating increase (not per HD) is a good way of
keeping a monster’s SR relevant.
Amin harmuva onalle e' cormamin
Amin khiluva lle a' gurtha ar' thar
Amin naa lle nai, a'maelamin
Cormamin niuve tenna' ta elea lle au'
