Maybe an attacker counts on that. Or possibly even rigs his near-c rock to explode so as to create a VERY precise doughnut. He might do so in order to sweep the 100D volume clear of all defence installations/ships (and incidentally everything and everyone else . . . an "Orbital Napoleon Omelette," don't ya know . . . ).

This would leave only those defences on/in the target world itself plus any placed outside easy initial engagement range to oppose his invasion fleet.

NOTE: I had a thought on meson guns, BTW. It might be that they're called "meson guns" because an odd quirk of jump physics makes it possible to project that *particular* subatomic particle through local jump space to re-emerge nearly-instantenously at precise coordinates in [relatively] nearby real space.