Does Coax Type and Length REALLY Make a Difference in a Mobile Set-Up?

[Cedar Mountain Radio]

Hi Vagabond,
I was reading the above posts and one thing I didn't see addressed was RF getting into the equipment by riding the coax back in and causing distortion or squealing in the mic. I found that coax loss isn't really the bigger factor in mobile antennas because the coax length is usually so short that the losses are miniscule, but to me, having a length that doesn't cause problems with RF feedback is the more important issue.
I find that using 17-18 feet of any type of coax often causes RF feedback problems and I attribute that to it being a half wave of shield and that puts a lot of voltage at each end.
I have done away with RF distortion by getting away from a half wave length or about 18 feet and going to more like 12 or 24 feet when I was getting distortion or squealing in the mic.
Maybe that helps.