I'm glad you've found a solution. It's a bit like driving at 120mph in a 30mph zone and expecting to turn the corners on the same 30mph line. In a word... impossible.

Hi twilfert There is another problem with using the acceleration feature in FS.Even if you pass over a straight line waypoint you may not receive a "credit" if someone else is talking.It may be the controller talking to you or another.Or even a chatter pilot reporting in.You do need to keep an eye on that RC dialog box.And listen for the ping. As Ray says tight turns over waypoints will often fail to be recognised if at 4X.