"overlap" is just wasted space in Burst. "overlap" means you have the same nonces twice.
Like in this example:
You have nonces 8 to 15 in file#1 AND file#2, as they overlap. File#2 should start at 16 or elsewhere, but not within [0..15] as it doesn't help mining.
The Botnet Master has "the problem" of coordinating some ~15k plotters.
Easiest: you start to plot at a random position.
That might produce some overlap like above between individual bots, reducing the overall efficiency.
But that "overlap" problem is negligible:
One nonce has 4096 * 64 Bytes == 256 KiB.
Assume you have 16k bots (~2^14).
Assume every bot has ~100 GiB free disk space claimed by the plotter/miner, the length of each plotfile is 409600 nonces ( ~ 2^19 ).
As the number of possible nonces for each account is 2^64, the chance for each new bot to overlap an existing bot is (very crudely)
2^(64-19-14) ~= 2^31, a chance of 1 to 2 billion.
So he does not waste any brain cycles for coordinating the plotting.