Path of Exile Dev Tracker

Returning is the "last" in the list of possible projectile behaviours when hitting a target. So it won't happen until all that projectile's ability to pierce, fork, chain, or split have been used up (in that order, I think - split might come before chain, but I don't think players can get splitting projectiles currently so it's been a while since that mattered and I had to remember it).

There are two forms of returning - this one is returning from a final target (the wording has changed in 3.8.0 to be a bit clearer - previously it was something like "Projectiles Return to you after Hitting targets"). This means it's an on-impact behaviour only, like pierce, chain fork, etc, and can only happen when the projectile hits something (and as noted before, it has to have used up all the other behaviours first).

The game also has the broader "Projectiles Return", which does the same thing but also has them return if they hit max distance. I don't remember if it works on col...

That specific support wouldn't work for an entirely different reason - it's a gem with a support effect and a skill. The support effect is passed to minions, like all support effects. The skill is not, just like all other skills from gems.

All minions. The supporting system doesn't distinguish at that level.

It does not add tags - tags cannot be changed.

It changes the behaviour of the skill so that the skill create minions.

Close Combat Support says "Cannot support skills that create minions"

That has never been the case

Making monsters have correct weapon types internally is something I would love to do, but it's also a massive task and the benefits of it don't really justify the amount of work it would take, at least for now. As such, stuff that cares about weapon type isn't able to work for minions.

I was pretty sure Holy Relics would be one of the things with a low aggro range, but it turns out they have a notably higher than average one. I assume this is to facilitate it targeting you for it's teleport skill from long distances.

Is it really so bad to just... make summons inherently aggressive

Most minions effectively already are and always have been. Aggressive was added for Golems, which were designed around a low aggro radius specifically. The new gem allows it for other minions as well, which is relevant for a few spectres of monsters with similarly low aggro radius, but the vast majority of minions gain nothing inherrently from the aggressive property because their aggro radius is already bigger than that. They do gain the other bonuses of the support (and can use it to cancel out the Defensive property of Meat Shield support if desired).

The thing you're asking for is what you've already had for a long time in almost every case outside of the Golems, which are supposed to be non-agrgessive by default and already had a way to be made aggressive.