Roy Lewallen wrote in
:

The EZNEC insulation modeling method is basically similar to that used
by NEC-4, but different. The accuracy is comparable. Both programs
(EZNEC and NEC-4) are accurate only for thin layers of material with
relatively low conductivity and permittivity, i.e., like typical wire
insulation. But since the typical change in effective wire length is
only on the order of 3% or so, high accuracy isn't required.


Roy, I went back and re-read Cebik's notes about the way in which the IS
card is processed vs using and LD card to add inductive loading. He
passes on an explanation:

===quote
In calculating the E-field for each segment in a model NEC calculates a
"cosine" component, a "sine" component, and a "constant" component. NEC
then sums the three fields to arrive at a total field value for each
segment.

LD commands modify the "constant" component of the E-field calculation,
whereas IS commands (in NEC-4) modify the "cosine" component. As a
consequence, any workaround formulation will result in satisfying only a
limited range of geometries.
===equote

It was with this in mind that I chose to head down the NEC4 path.

Owen