Miscellaneous: Shrunken Goblin Skull Earring effect not working properly?

[Pokingmon]

This is more of a question than a bug report...

I may be missing something, but the description for Grim Aura's effect is "Increase ATK by 7 (L4) to 10 (L10)".

I'm currently getting an increase of +7 (unbuffed and naked) and sometimes +6 ATK (depending on my current buffs) at level 48. First of all, what makes for this discrepancy in ATK increase?

Second, shouldn't the ATK increase be at least +10?

I know that the insta-cast buff slot is part of the appeal for dispel, but I'm curious about the actual buff.

Again, sorry if this is a dumb question, I may very well be missing something. Thanks.