For a start, I would limit the maximum power to 7.5 joules as that will permit Germany and other continental countries to take part easily. Anyway you don't need 12 ft.lb to knock over a reset target, not even half that, and there's still about 50% energy retention at 55 yards.
Second, I'd cut the maximum range to 30 metres, that will free up lots of smaller plots of land to set out courses that at the moment they haven't got space for.
Kill zones would all be reduced as well.
So the combination of lower power and smaller kills will compensate for the shorter distances and mean that wind is still a factor to take into account.
I'd probably set a minimum scope mag to be used, yes a minimum. With targets only out to 30 metres rangefinding becomes too easy, so a minimum scope mag it is.
Also I'd have targets where the kill to hinge distance was variable (hint: my club is developing such an evil device.....
) - not just say two options but a variety of permutations.