It should matter. Every idiot should be able to see a big red ball hanging around in front of you.
There would be a nice way to make this irrelevant - give the mines a cloaking device. They will still be large, but faded away, invisible.
I also wonder what Vasari mines would be like.
How their hi-tech phasing mastery gets reflected in them.
well, just a thought here, but what if say, a phased out particle was hot thru an anti-grav field, creating an explosion.... hey, just a thought!
anyway, the Vasari would probably be like rounded diamonds or spiked spheres. as for phase tech, it could actually be phased out (Jikarta Navigator's phasic cloaking ability turned on by default w/ no antimatter cost, then phases in to activate the mine when a magnetic/gravitic sensor detects a ship nearby).
oh, and I think large clouds as a single unit would be a great idea. and magnetic attractors so that the mines moved toward something if it got close enough.