You can always suspend the dongle from the cable 
Don’t misunderstand, i’m not saying RG6 doesn’t work, just that the loss is higher when you use it.
A flexible pigtail is unlikely to add more than half a dB of loss, probably less.
Don’t overthink it either, if you are trying to optimize every last bit, you soon start thinking about the large DPD antenna (which gives very nice results).
What is more affordable and in my experience gives better results than the prostick+ is the rtl-sdr filtered LNA with the v3 dongle (or an airspy mini if you want to spend extra money).
You should also check this: What is the Maximum Range I can Get?
If your maximum range is 180 nmi or less, gear doesn’t matter that much any more. Then you run into the terrain limitations even with a mediocre setup.