This has to do with the penalty values for lower order roads and the priority values for the several road types in the routing.xml
No highways means that it will still try to find the highest priority roads except highways,
"do not avoid" is something else than "prefer" (unpaved roads).
If you create your own (renamed) routing.xml (the default routing.xml contains multiple profiles) and upload that in your own OsmAnd, you can completely destroy the smart optimized way-find algorithm and it will then simply use any road that gives your the shortest distance.
You could copy the "auto profile" and remove the rest and renamed to "myshortestway.xml" and do not forget to rename the profile name itself.
Also search in the blogs and technical articles on
osmand.netThen search this mail thread. I once or twice wrote, at least a year ago, how I created them.
Harry