Hi Peter it is a difficult ask for an ideal distance other than 500m because there is nothing like hitting a postage stamp from 500m away,
However if distance is a problem then i think that 300m is just as trying with a reduced target Pete Vanmuers put together the mossy target and it is difficult enough and you truely see your end result pertaining to wind reading and mean point of impact of your handloads.
Another way of practicing is with a Rimfire at 200m, now that is a true challenge although you are at the mercy of the ammo with this type of shooting but it does hone your skills with wind reading.
I think that to practice the fly you need to shoot the full distance, I don't practice the fly at all i only shoot at matches, however i do shoot groups, with short range Benchrest, practice my wind reading with full bore target rifle and F class so i get a reasonable amount of trigger time.
When you get to a match watch what the front running shooters are doing it is the little things that make the difference like setting your rear bag and benchrest up properly, making sure your rifle is tracking onto your aim point every time it returns to battery little things like that make all the effort worth while.
good luck
Les
shooting well is more a mental control of your thoughts than just pulling the trigger........