Nipple size on main vent?

mitch101

When is a main vent nipple too small to take advantage of my two Gorton #2s? My Crown BSI103 steam boiler is oversized based on edr and short-cycles, so I threw out the old single vent and made an elaborate antler to hold two Gortons as in photo. The Gortons are 1/2" but the nipple is like 1/4" hence the nutty arrangement of adapters to downsize and hold them vertical. The nipple is on the elbow of the return, at the turn of a 30' pipe leading to the final return. System is single pipe.

Steam reaches the farthest radiator pretty fast. The Gortons do rattle when cold. They do seem to release air and close when hot, but half the radiators hiss upstairs and the boiler short-cycles while thermostat keeps calling for more heat. I lowered pressuretrol to 1.5 with a 1.0 subtractive diff after having it much higher (which was inefficient, I know).

Should I hire someone to tap a 1/2" hole (wall thickness concerns me), or else weld a 1/2" threadolet on, then plug the tiny 1/4" one? Or is 1/4" already big enough to release all the air that needs to be released? My goal is to fix the short-cycling.