Problems with tapered wire radii?

I'm trying to find out why I'm getting an apparently bad solution
when modeling a quarterwave monopole over a PEC ground plane where
my monopole is modeled as a single conductor with tapered wire
radii at the base.
I'm using NEC-4.1, which as I understand it has less strict
modeling guidelines for tapered radii and for extremely short
wire segments (i.e. I should be able to get away with segments
on the order of 10E-5 wavelengths long since my seglength/radius ratio
is well above 2.0). I am having the code compute the average gain with the
RP card, which should be 2.0 since I'm using perfectly conducting wires
and a PEC ground. I successfully get 2.0 when I don't taper the base,
but I get a value of about 1.6 for one tapering scheme and 1.69 for a
second more gradual tapering scheme. In the first tapering scheme I
Does anyone have any suggestions for me? I've appended my model
source files below.

Thanks for any input you may have,

Bobby Cox
Staff Engineer
Kintronic Laboratories
(bcox_at_kintronic.com)

********************************************************************
CM This is the 1st scheme that tapers radii upward by a factor of
CM about 1.92 from one segment to the next and length upward by a
CE factor of about 1.63 over 7 segments. It computed average gain of 1.604.
GW 2 1 0. 0. 0. 0. 0. 0.0508 0.002588
GW 3 3 0. 0. 0.0508 0. 0. 0.2032 0.002588
GW 4 7 0. 0. 0.2032 0. 0. 2.577355
GC 2 0 0 0.002588 0.128016 0.0508 1.0
GW 5 47 0. 0. 2.577355 0. 0. 48.768 0.128016
GE 1
FR 0 1 0 0 1.68
GN 1
EX 0 3 2 0 1000. 0.
RP 0 46 2 1001 0. 0. 2. 2. 1000.
EN

***********************************************************************
CM This is the 2nd scheme that tapers radii upward by a factor of
CM about 1.144 from one segment to the next and length upward by a
CE factor of about 1.108 over 30 segments. It computed average gain of 1.692.
GW 2 1 0. 0. 0. 0. 0. 0.0508 0.002588
GW 3 3 0. 0. 0.0508 0. 0. 0.2032 0.002588
GW 4 30 0. 0. 0.2032 0. 0. 10.
GC 2 0 0 0.002588 0.128016 0.0508 1.0
GW 5 40 0. 0. 10. 0. 0. 48.768 0.128016
GE 1
FR 0 1 0 0 1.68
GN 1
EX 0 3 2 0 1000. 0.
RP 0 1 73 1000 90. 0. 0. 5. 1000.
RP 0 46 2 1001 0. 0. 2. 2. 1000.
EN
Received on Thu Mar 28 1996 - 16:03:00 EST