The problem is that they may not attack the closest target, and instead attack a more distant one, moving into range of another turret in the process.  As Deceiver says, you can queue up targets manually to ensure this doesn't happen.  Scouts can be bad about choosing which mines to disarm, and can run into other closer mines in the process... they're particularly bad about Advent homing mines and basically NEED to be manually managed.

This has all worked very well thanks - but I must say I find fleets clumsy

It woul be very nice if each fleet was colour coded in the ship list, so you could see at a glance which ships were in which fleet and which ships were not in a fleet

And then if the tactical fleet markers showed the same colours you could tell instantly what you had where. I find myself looking for the sentinals fleet when I need it, after another a new batch of homing mines appears etc

The mechanics of Sins have been done very well, except that tactical combat is harder to operate well than it needed to be.

Any thoughts, have I missed anything?