Frap - I believe that resistance played a part in the added 2 feet, and inductance as well. The 16 gauge cable 2 feet long can have the resistance of 20 feet or more of 14 AWG ROMEX. It has the inductance of about 12 feet of ROMEX. So this was like adding 20 more feet of ROMEX to the circuit.
I agree with you on the air dielectric being the best, however the goal with a power cord is low inductance and resistance. This means large conductors or lots of smaller conductors that are tightly magnetically coupled. Some cords do not do this coupling well and the result is excessive stray magnetic fields. Power cords do not "pick-up" stray fields, but they do create them. If you have unshielded interconnects running side-by-side with a power cord to an amp, you might pick-up some magnetic crosstalk in the interconnect. Incidently, shielding a power cord is a bad idea, IMO, because it adds unnecessary capacitance. Typical shielding also will not stop the stray magnetic fields for the most part. You need MU metal shielding to do this.
I agree with you on the air dielectric being the best, however the goal with a power cord is low inductance and resistance. This means large conductors or lots of smaller conductors that are tightly magnetically coupled. Some cords do not do this coupling well and the result is excessive stray magnetic fields. Power cords do not "pick-up" stray fields, but they do create them. If you have unshielded interconnects running side-by-side with a power cord to an amp, you might pick-up some magnetic crosstalk in the interconnect. Incidently, shielding a power cord is a bad idea, IMO, because it adds unnecessary capacitance. Typical shielding also will not stop the stray magnetic fields for the most part. You need MU metal shielding to do this.