its my only complaint with them. if 1 sledge can attack an enemy and the healthbar goes away and then blinks back in when it shoots again it adds a lot to the visual noise of the fight.
give the healthbar a check of its attacker's attackrate, if the attack rate is longer than the default hide delay of the healthbar then set the delay to the attacker's attack rate instead (plus some for projectile travel time)

(and/or give us an option to set damaged healthbars to be permanent like in all RTS's)