Yes, even with the hammer cocked, it is still lowered down below the disconnector sear on the rear ward stroke, hence riding the bottom of the carrier.

Carbine recoil spring should be around 10.5".  

If you pull the spring and find that it is around 11.75", then you have a standard spring installed (read spring is too long/binding up before the buffer bottoms out on the back of the receiver extension.

Shotgun you action open and take a look at the disconnector/trigger just behind the hook for a dent or white line.

What may be happening is the hammer tail is binding on the top of the trigger/disco as the carrier’s lowers and moves a crossed it on the reward stroke.

If you find this dent/white line sign of carrier/hammer wedge, then remove around .040 off of the tail of the hammer to prevent the problem.

Bottom line is with the hammer uncocked, and you pulling back the charging handle slowly, there should be most of the resistance until the bolt unlocks, then slightly less as the carrier moves back and cocks the hammer, then from that point back, the least amount until you can lock the bolt back.
Note: Recoil spring tension will be a constant, just the different phases of added tension.