Raised on the Erie Lackawanna Mainline- Supt. of the Black River Transfer & Terminal R.R.
I did not understand the specifics of the feeder length and the relationship to resistance, only that shorter was better so that's what I strived for. Even using 18 gauge for the drops, I kept the length to 8 inches at the expense of a lot of lower back discomfort after the wiring sessions. If I were to do it again, I would keep the gauge but not be so anal about the drop length.
I like the idea of the bus along the facia and there are certainly numerous ways to dress or even hide the wires available.
I am member of the Olde Newburgh Model RR Club. Several years ago we installed a digitrax DCC system on our layout. The previous DC wiring was 18 AWG and had many areas that were farthest from the controllers that had some voltage drop problems. I began rewiring the DCC buss on the outside of the layout using 14 AWG stranded wire and European style pass through barrier strips, stripping the insulation off the wires where they pass through the barrier strip. Then the rail feeders 20 AWG stranded, were brought out to the buss and inserted in the respective barrier post. This system is called a buss duct. This made working on the wiring easier as it eliminated the task of crawling under the layout and working upside down. I then made a new facia for the portion I have completed to cover the wiring. The buss consists of four power districts running in the duct. I have completed 30' of this duct and it looks very nice and has replaced the rats nest of wiring under the layout.
By the way, a former member of my club, an NMRA member, called this ridiculous and that he had never seen this done before. He is no longer a club member thankfully.
As Selector indicated, "Short," is relative.
I wire all of my electricals through terminal blocks designed to be reached while sitting on a chair in the aisleway. My longest drop, rail to terminal block, is about one meter. Others are shorter, down to six inches or so. (I still use Analog DC, but the terminal blocks are where I would put my main power bus connections if I ever switch over to DCC.)
Glancing at the AWG table of wire sizes/current capacity, #14 bus wires have a resistance of 0.0083 ohms/meter, and #18 drops have a resistance of approximately 0.02 ohms/meter. If you protect your circuits with the tail light lamps everyone recommends, you will never come anywhere near their rated current capacities.
Adding a few centimeters of length to rail drops to bring all the connections to the edge of the layout is a good investment in long-term satisfaction.
Chuck (Modeling Central Japan in September, 1964 - with easily-accessible wiring)
If you can be neat and organized, keeping your orientation consistent between left and right rail with a given pair of feeder wire colours, I don't see a problem. And even then, why not use the same gauges you talk about?
I have several sets of feeders to my folded loop 56' main. Some are a few inches, some are 3'. To me, the idea is to have a 16-14 gauge bus running around the layout so that feeders can be kept "short". Short for 24 gauge wire might mean 12" for 8 amps. Or, it might mean 24" for 22 gauge and 8 amps. I use the four wired cable that you buy in a 100' spool at Radio Shack. Each wire comes in a plastic sheath of yellow, black, green, or red. I think it is 22 gauge, but I can't remember. Whatever it is, I have one 3' pair feeding my staging yard, all 30' of it! I do have a tail light bulb wired in series before that pair of feeders, and when I get a staggered engine somewhere on the staging line (it has happened...), that light glows every time and takes care of any worries.
My bus comprises what would have been discarded braided speaker wire, fairly heavy stuff....maybe 14 gauge.
A good bus, lots of feeders, and keep them as short as practicable. Just don't be pathological about it all.