I read that runs of RG11 that are less than 100' long can run into problems with reflections. RG6 and RG59 are less susceptible to it.
Micro reflections. Umm, yeah, I've heard that you should avoid using less than 2 foot cables to interconnect equipment. The impedance match isn't perfect and a short cable length can cause the reflections that will occur to interfere with the digital QUAM signal. Supposedly anyway. Never heard anything about what you are saying. Wouldn't make sense.
Yes, unused splitter ports should be terminated. By the same token unused wall plates off those splitters should be terminated too- but they never are.
-Hal
