I think the key is femur length. If you're 6'4" but have the Michael Phelps body type (all torso, short legs) you might fit in the seat just fine. I'm 6'1" an

I think the key is femur length. If you're 6'4" but have the Michael Phelps body type (all torso, short legs) you might fit in the seat just fine. I'm 6'1" and have the opposite body type - short torso, long femurs - and the seat pitch in Delta economy is uncomfortable to me, so much that I usually pay the upgrade for Economy Comfort.