Your Offshore boards should handle 3oz weights with only the tail of the board sitting low to being under the water surface without a problem. 4oz is a bit to heavy and the boards run different than when running 3oz and lighter.
Like mentioned, if you use #27? rubber bands ( standard office size, and cheap) you should be able to run 3oz weight without the flag going down at all. I do on mine. I snipped a small "<" notch in the front of my boards at the highest spring hole. That notch will hold the rubber band where ever you place the tension.