we've worked out that with a transparent acrilic plastic, where we drew a circle, and some of the typical lines. then you try lets say the avalanche and your caller is seeing the loop thrugh the acrilyc and knows if the shape is going well. good thing is that if you fly alone (ok or lets say with somebody who is not an f3a enthusiast or pilot) he/she can help you with this as it needs no training or knowledge.
some other things we've practiced is to have somebody at 150 to 175 meters (exactly below the flight depth) with a cellphone and the pilot wiith a hands free device flying and receiving instructions such as "youre going in, or you are too far out" i found this really helpful as it is very difficult to keep depth even making straight passes with no maneuver. i did this with some top pilots in RSA WC and believe me... there is a lot of depth changes "even on the best families"
And last... i'm waiting for an eagle tree to test.
But in the end. it is all about practice.
regards
Marcelo