Because of that soft-flux dissipation, the fortress shield allows the Paragon to stay in combat with shields up waaay longer than other big ships can. When a Conquest or Onslaught is firing all its weapons, it maxes out flux in a matter of seconds and has to drop shields. The Paragon, instead of dropping them, can switch them to fortress mode, wait for all the soft flux to dissipate, and then go back to regular shields and pound out a few more seconds of fire. You can repeat this several times in a fight; it allows the Paragon to absolutely crush other capital ships in one-on-one (or even one-on-two or one-on-three) combat.