Thanks, guys. Hadn't dug up a Cake man page yet, appreciate that. And Moeller0, think I've read you before on this, thanks. Now, who gets to notify the docs people here on the LEDE and OpenWRT sites? 
A few more questions. I've been mostly using luci, so not so familiar with what it writes, as well as not so familiar with the process of manually inputting. Just starting to do tc -d qdisc and begin to understand the outputs...
So, sounds like with luci, setting "Ethernet with overhead...." and 18 bytes would do it for Cable Modems? Or is it different or better to do your manual command?
Second question, how does one enter manual commands, and set them up so they are there at bootup, if not using standard luci interface stuff?
I have another issue with my UL behavior, but I think it really belongs in it's own thread, so I'll save asking what various tc -d and -s outputs mean, and what might be better settings than what I have, for that...