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when the chain gets installed adjustment is needed to get the tension correct, thus already losing valuable adjustment .
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I dug out my caliper. The distance from the rear axle to the bottom bracket can be shifted by a half inch with the Nomad eccentric. I think (but do not know for sure) that the Raven uses the same eccentric.
Since a chain consists of half inch long links, I suspect that the eccentric was designed that way. Thus, if you used up too much adjustment when a new chain is first installed, you should still be able to remove a pair of links (one inner plate link and one outer plate link) to shorten the chain enough.
That probably is not an ideal solution, your saddle would suddenly be a half inch too far forward if you move your bottom bracket back a half inch. If you adjust the saddle rail position, then your handlebars are too far away from your saddle. This likely is something most people would like to avoid.
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There must also be a certain chainring/sprocket combo that would ideal that when the chain is replace the tension is near perfect, so when the BB is at the end of its stroke, the chain really is worn.
The "ideal" combination of chainring/sprocket would also vary with different chainstay lengths. I did not check the Thorn specifications, but I assume different bike models and possibly different size frames have different chainstay lengths.
I suspect that there are many "ideal" combinations, but how you define "ideal" may vary depending on how much stretch you want to have before replacement. Derailleur bikes, I try to change the chain at 0.75 percent stretch. On the Nomad, I am still on my first chain, but I will probably also use a 0.75 percent stretch criteria for that bike too.
So, I do not think "ideal" means you need to have the bottom bracket in the rear-most position on a new installation, you just need to have enough adjustment remaining that you can take up all the slack you expect to need before chain replacement. And the Nomad being an expedition bike, you probably would want a bit more adjustment available in the event that you can't find a new chain while you are in outer Mongolia.
Last time I checked, I was around 0.5 to 0.6 percent stretch on my Nomad, so I am getting close to replacement time. But, I think I have enough adjustment left in the eccentric to make it to my goal of 0.75 percent.
My Nomad (size 590M) has a 44T front/16T rear and has 104 chain links (52 inner plate and 52 outer plate links). Sometimes I use a 36T chainring instead, then I remove four links. (I also have to adjust the eccentric slightly when I switch chainrings.) Thus my chain is 52 inches when new, or 50 if using the smaller chainring. At 0.75 percent stretch, the chain would be 0.375 inches longer when I want to replace it. Thus, I need a range of adjustment of about half that, or about 0.1875 inches, that is well under the half inch range provided by the eccentric.
I suspect most people will run their chains longer than me. I would rather replace cheap chains than have to also replace the rear cog too, that gets a bit more pricey. (Yes, I know I can turn the cog around to get double the wear.) I buy the cheapest KMC chains, I can get two or three new chains for the cost of one rear cog.
I am using the word "stretch" here, but the metal plates in chains do not actually "stretch", a chain gets longer due to the bearing wear in the links, so I hope my use of the word "stretch" does not cause confusion. Maybe I should have used the word elongation.
