Rifle Scopes trijicon 5.5x50

[Sorefoot]

I'm very confused. I switched from a trijicon 4x32 to a 5.5x50. The smaller scope is a lot clearer and brighter. I've heard good feedback on the 5.5 for longer distances. I am consistent at 600yds with the 4x32 and I'm struggling to see 400yds with the 5.5.

P's both are calibrated for .308 and we're and are on a Ar 10.
Thanks in advance on any help.