Hoping for a few tips on breeding these guys. After a bit of bad luck and losing a few cocks (but not any hens???

The lowest I have brush on the walls is maybe 1m above the ground, as I don't want to make it easy for anything that may get into the aviaries somehow to get up to nests. Is it worth me devising some other way of supplying dried brush lower down in the aviary for the pictas? Also, what is roughly the minimum size of grasses to be useful as nest sites? I currently have the bigger grasses tied up so as to provide more dense, upright cover, rather than more spreading.
As usual all my birds get a good finch mix, extra pannicum, soaked seed, maggots, leb cucumber and green seed (when I have it, ran out about a month ago), as well as the usual grits, calcium sources etc.
I've heard they can be frustrating, and they well and truly have been so far, but the 2 males seem to have chosen their hens, and have caught one of them displaying a couple of times now (awesome sight to see, will try and catch it on camera some time) so am just hoping that there may be something I can do to give them a nudge in the right direction for this coming spring.
Cheers in advance
Luke