Fast restart should only be a problem if you have moved the tractor and answered "no" when it asks if you have moved the tractor.  I usually lose XP convergence when travelling on the road and drive under trees or by a tree line.  I've noticed that it is slower to get convergence back when you are moving at higher speeds as opposed to sitting still or slower speeds.

You can raise your convergence higher and keep it longer.  I use 24 inches for planting and 30-36 inches for everything else.  My unit was initially set at 12 inches and I couldn't keep convergence well at all.

Ditto on the need for 5 or more satellites.