We would be if posters weren't offering a selection of brightly colored herring in the form of voice/data, emergency and medical communications band distractions.Since this is a thread about ATSC 3.0, I think we're safe.
While they may call Portland their home market, some of the towers are located as much a 45 miles away. The LA stations are packed in like sardines to be sure but I wonder how much of their 6Mhz they can actually use. While the use of guard bands between different types of services may seem obvious, there needs to be a certain separation between channels using like modulation schemes as tuners aren't perfect.I gave you co-located examples in Portland, which I thought you would be familiar with given your location.
I read where Sprint once used a 625KHz guard band both above and below its 1900KHz LTE services. Out of the 5MHz they were given, they could only use 3.75MHz. I read where one of the more recent schemes could pass 4.5MHz but that's still a 10% forfeit.