I have chased and ridden C&TS and D&S photo trains since 1971. I chased the Toltec Rattler in 72 and have done Trowbridge, Wimer and Friends charters on the C&TS and have done many Railfest specials and photo charters on the D&S. I have seen both sides of the debate (dispute). Riding and/or chasing both offer great experiences and opportunities. There have been disputes between chasers and riders, but I have also seen disputes among riders about photo lines and locations. There was almost a brawl on one Friends charter I rode.
I have a suggestion based on what Yvonne Lashmett (box car betty) did on the D&S. Her photo trains were well planned, well organized and well conducted. Crews went out on motor cars a couple of days before the charters and laid out photo lines with police line tapes. Riders were required to shoot from the photo lines, if the location was too small for everyone to get in the photo line, she arranged for half the folks to shoot first and then a second runby is performed giving the second half an equal change at good shots. The D&S is not accessible by vehicle the way the C&TS is, so not many if any chasers.
Having the runby locations marked with tape, any chasers could see where the photo lines would be and could avoid parking vehicles where they could be seen. Also the chasers could find spots that would not interfere with the riders.
I have been on team putting out tape lines on the D&S and the locations were varied from year to year so return riders could get different views.