High level skill xp penalty question

Warning you will get reduced experience while training this skill because it is at or above your current level.

Two questions about this reduction:
1) Is it a constant reduction rate, or does the reduction rate increase as the skill level gets further above the character level?
2) Does anyone know the specific reduction rate or the formula that determines that rate?

[Sapreaver]

it is an exponential formula I know that much the higher you get above your char the bigger the reduction at about 10 levels above you are getting 5% ish of normal exp

[Chrism]

Its not exponential, its 15% at 1 level above, 20% at 2, 10x level difference at 2 - 9 and it caps at 95% penalty for skills more than 10 above char level from what i've seen