use a container. and/or an on created command that pins em there. 1 line of code would do it.
give the turrets greater range.
or, to differentiate between smaller and larger targets, use two turrets on top of each other, one with larger objects for targets and a bigger range to make up the difference.
there are a lot of not that difficult ways to fix this.
but maybe you're right. maybe there is a better way. but it seems, to me, at least, that checking for one point, on what would presumably be a good number of targets, is going to run a lot better than checking the whole collision box for all of them. That's just my best guess as to why it is that way.
Whether it's a bug or not, I'm just letting you know, it's not that difficult to deal with.