I have a graco carseat base in my HCH-II as well. It's hooked up in the center of the backseat and is attached to the LATCH system. I'm 6'3" and don't have any problems with the car seat even though I push my seat all the way back as far as it will go and usually have it reclining one tick.

Heck this weekend we had a whole boatload of people in the HCH-II without a problem.

My wife was driving, she's 5'5".
I was in the passenger's front seat 6'3"
My mother-in-law was behind me 5'2"
My baby was in the middle in her rear facing car seat.
My sister-in-law was behind my wife and on the other side of my baby. 5'10".

We were all amazed at how uncramped things felt even with all of us in the car. I think we were actually quite close to the maximum load rating hahaha

just my .02
Jayson