Somewhere along the line, I picked up the idea that it is better not to have elastic in a breastplate that is being used to help keep a saddle in place (as opposed to being used just as an anchor for a running attachment, for example, or just as an oh-sh** strap). The reason being that the elastic (obviously) allows some amount of stretch/slip, at which point it’s pulled too tight for general comfort. Better to have a properly fitted leather breastplate that is stable.
True or not (in your experience/learning)?