Try a finger spool in place of a reel. Mark it with a pernanent marker at ~ 20’ and clip it off. the reel and the clip provides the weight and a focal point for a mid water safety stop.
If your mid water deploying the spool at ~ 50-75’ will also allow extra time for the SMB to be on the surface and the boat to see you. The sooner the better if you find your off the ascent line.
While the reel does add to the weight your carrying ALL equipment counts to your overall buoyancy control. If you add the reel, take away 1 or 2lb from the belt to compensate the same as you woul ddo with a light or other equipment.