" I have a question about adjusting the low and high limits. I noticed that with my bike, there is maybe one point along the chain that seems to run closer to the derailleur than the other links in the chain. For example, as I stare at the chain while I'm turning the crank slowly with my hand, I see that for most of the links, there is adequate clearance between the FD and the chain. However, as I approach one point along the chain, this clearance decreases and there is one point along the chain where the clearance is at a minimum."
I'd look for a bent chain ring.