I forgot about upkeep, right:(... So it's actually about 2000 dissipation (while we are at it - how about rounding absorb coefficient display to 1/100? 1/10 seems too rough) .
I agree that described above behavior would make sense, if it actually did have chance to fire - but in my test it doesn't: i outrange all, but lance due to optics + targeting unit + keep my distance, and it won't fire lance since i keep shields up.
It activates Fortress shield while not firing any weapons, despite having about 200 spare capacity (i keep flux at zero for test purpose, so no bonus involved). Point about it losing because of fortress shield still seems to be valid (or at least losing much faster than it would otherwise, since i'd have to build up flux to actually overpower it).
Actually, even if we assume that 1800 is somehow borderline enough to get through it's regen under these conditions, build up rate would still be less than 600 that it gets with fortress shield.