I'm fighting 3 ghouls in the Moathouse and noticed that the AC of the ghouls seems to change somehow.

My rogue hits with a longbow and when I check the rolls the AC of the ghoul is reported to be 18.
Then my sorcerer does exactly the same thing with her longbow (elf) and when I check the roll, the AC of the ghoul is reported as 14.

Now my rogue has Precise Shot, so she doesn't suffer the -4 'Firing into melee' penalty, yet that penalty did apply to the sorcerer's hit roll, but the AC was reported as being lower.

Is this a bug? Does purchasing 'Precise Shot' merely pass the -4 penalty off by adding it to the target's AC?

I should've learned from my previous lesson about BAB.
When I checked the AC is was showing a +4 bonus due to cover.

I'll have to use 5-foot step more frequently in order to avoid that penalty.