do the M4 feed ramps in barrel chamber affect front sight height
installed in a non-ramped, standard upper receiver? If so, is it
a significant amount?
The feed ramps have absolutely nothing to do with p.o.i., unless they mitigate bullet striations during feeding, then you'd be talking about groups, not p.o.i.
The only problem you would really run into is if your receiver is cut for M4 feed ramps and your barrel extension isn't. Then you could experience jams or marring to your bullets during feeding.
