Healing Spell Power in BGs is reduced

So pretty much what the title says, same gear, no buffs, doing 4.4k flash heals outside a BG. When I enter one, I do 4.1k same gear no buffs. Is it suppose to be like that?, It's like losing invisible spell power. Been testing it and its the same outcome every time. I mean if it is suppose to be like that then its fine by me, but if it isn't and I'm the only one then that's unfair. Do BGs give invisible debuffs? Can someone enter a BG and test there healing too to see if its the same.

Edit:
Tested on my shaman, doing 7.7k crits, 4.5k lesser healings and inside bgs doing 7k, 3.9k heals
Does this go for dps as well?

https://wow.gamepedia.com/Battleground
Patch 3.3.2 (2010-02-01): All healing abilities (including items such as potions) will be decreased in effectiveness by 10% when in Battlegrounds, Arenas, or Wintergrasp.




This does not apply to damage done.