Just got the "clear wait points" logic to group-move each planet's chunk of threat towards its target wormhole, so that deals with one of the downsides of "don't camp right on the wormhole, you moron".
The other is that right now I've got them waiting either at the wait-planet's command station or at a point selected in a way similar to adv-fact placement: near the inner grav ring, as far from wormholes as possible.
This does reduce the threatball's defensive utility (they'll FRD into attackers from there but it can take a while to get in-system) but I don't mind that so much: the AI's priority for these should probably be "conserve until I can use them offensively", and leave defenses to the guards and the SF and such.
The actual problem is that it can take quite a while for the threatball to actually reach the wormhole once the "stop waiting" order comes down. It can also take a pretty variable length of time for one planet's threatball to reach the wormhole compared to another planet (that was waiting against the same target, for instance).
So I'm thinking that they need to pick a closer spot to the wormhole.
My question to y'all is: what range?
In theory it could be variable (based on "does the human have a black widow golem?", probably
) but I think a single global range (or range of ranges) would be better for a first try.