Jim Weir's COM antenna

Hi Jim,
sorry for bothering you on this one again, but I'd like to understand
how
radios/antennas work..or don't work.
Since my last mail, I found I had a bad BNC connection, I replaced it
and
for a while I thought I solved my prob of high reflected signal power
(it was 7 W out and 5 W reflected, on the whole band, worsening with
high frequencies).
Recently, the same problem appeared again. My radio KX 155A receives
well at any time and distance up to 50 miles; it transmits well on the
ground and in the air till I stay within about 5 miles from the
airport.
Then, as I fly further, when I transmit, my comunication is received
broken
and what I see on my radio's display is a continuous flip-flopping of T
and
R while I push my PTT .
Maybe it's again too much reflected signal, but what I don't understand
is:
why only when I am at a far distance from a receiving station? It seems
that the presence of a receiving station (antenna) within, say, 5 miles
hides my malfunction.
Could this be the explanation of this weird (for me) behaviour?
What is likely to be the cause of this antenna malfunction? My radio
was bench tested OK.
Thank you very much.
Gianni Zuliani