Monster Advancement and XP rewards

[Bagpuss]

If you say advance a monster from 6 HD to 8 HD how do you calculate its XP award?

 

[Destil]

It's weird. It's not mentioned in the advancement block in the MM in the first printing (oversight, I don't really remember if it's in the eratta or not). But check out DMG 102 under the heading Tougher Monsters:

If you increase the HD 50%, increase both the XP 50% and the CR by 1.
If you doubble the HD doubble XP and increase the CR by 2.

 

[Bagpuss]

So I'm guessing XP by 33% and no CR increase.

Does the CR increase effect XP or is it just for EL calculations, it seems odd to add additional XP via two methods at the same time.