John, N9JG wrote:
When a wire flattop is fed with parallel line, what are the affects on the
system when the feedline is not perpendicular to the flattop? It would seem
to me that the system, consisting of flattop and feedline is no longer
balanced, and the feedline will radiate on transmit and pickup local noise
on receive.

That's correct. Common mode (unbalanced) current is induced into the
feedline by the unequal radiation from the two halves of the antenna.
This also occurs with an off-center fed antenna even if the feedline is
perpendicular, and with coax feedline.

Roy Lewallen, W7EL