Network Discovery command on 900HP Pro's

I presently have 12 Xbee 900Hp Pro modules and with Network discovery back-off (NT) set to 13 seconds, it will miss 1 or 2 modules in it’s discovery about 1 out of every 5 times I issue the ND command. I have to change NT to 30 seconds to reliable get them all. Is this time reasonable? I may very shortly be moving to 50+ 900HP’s. Should I then have to further increase NT? All parameters are at default but NI,NT and API.

For network of 12 modules, 30 seconds is more than sufficient. In fact, this should be fine for network of 50 nodes as well.

Thanks for the response. Appreciate it.