There's another trick up my sleeve.... If a low repeater hears a packet, I think it's prudent to increase the TX delay on it. The idea is to have the tall repeaters relay the packet asap. Then later if the low repeater decides to transmit, the higher repeater can decide if it's heard that packet before and NOT repeat it.

When I say low or high repeater I mean <50ft or >100ft. Naturallly this will vary by your individual circumstances and network topology.