Howdy. The trail length setting is absolute; it pays no heed to the train length. It causes Train Trails to look odd when you have LL-CCCCCCCC-LL along with L-C-L trains, as either the latter has absurdly long trails if you want to make the former look good, or you end up with the reverse, the trail ending before the end of the long train.
Ergo, my suggestion is have the "length" be relative to the train length, so a "short" setting of a long train or short train, both with the same speed, will roughly have the same length of trailing tail.
