Was your blockbehaviourconfig.xml modified at all? Schema set it before so that updated configs would not overwrite custom ones, because you could guess how annoying that would be for those playing with complete customs.
If you are playing on a server, you might have to ask an admin about it. I know EE ran a custom config (which already had shields doubled), so any of the config chances would not affect that server.
If you check your configs in starmade/data/configs/blockbehaviourconfig.xml, the line "ShieldCapacityTotalMul" is the value that controls the amount of shields gained per block.