DCS observation I noticed

When I was trying to see how many trains I could run simultaneously, I too utilized the "All" command.  I did not try what you described; however, I utilized the ability to adjust the slack between the consists by just adjusting their speed by individually addressing an MU or mult-header consist.   I had the fastest consist first followed by slower ones until I got to the slowest at the end. I would start them with the "All" command and then I individually just speeded up the slowest by 1 smph or reduced the lead consist by 1 smph when the slack between trains required adjustments.  In my case because I have several Kline and Lionel engines converted to Proto2/3 with several loops that require significant smph speed differences to maintain similar speeds.