Game Mechanics: Offense and defense skillups on a caster?

[Ropethunder]

I am a level 13 enchanter and my max skill cap is 70.

Despite heavily meleeing and tanking in every fight my 1hb is 42, defense is 54, and offense is 52.

No matter how hard I try I can't get 1hb over 42. I switched to piercing and easily got skillups from 33 to 42 within two or three fights. But after 42 it stopped.

From what I understand, casters should be able to skill up offense to 5 points less than the cap (I don't know if defense has this cap as well).

Why is it that these skillups seem to hit a brick wall when they're well below the cap? As soon as I level up I get skillups easily until I hit a new brick wall.