Bryan,

 Of the earth return loss resistance, how much of the resistance is the
actual earth rod(s)-to-soil contact and how much is the earth path ?

that is a very interesting question but it is difficult, if not impossible, to
give an exact answer. However, in a typical amateur antenna, the earth
path is responsible for a considerable part of the total resistance.

I believe in G3AQC's "footprint theory" - the more ground area covered by
the top loading wire(s), the better. More lawn in parallel, so to speak :-)

With an  inverted L antenna ,  is not a counterpoise of the same length as
the horizontal section and directly underneath but a few feet off the ground
a good way of avoiding the earth rod to soil contact losses ??

I have tried such a ground wire with an 15m up / 85m out inverted L but there
was no detectable difference. Feedpoint resistance was around 35 ohms
in both cases (including coil loss etc). Probably because the wire "catched"
only a fraction of the total E field. I did not try using the (slightly) 
elevated ground
wire as the only ground ("floating antenna") because I ran out of loading 
inductance...

73
Johan SM6LKM