Its not the incoming air, its the air in the crankcase. In normal rotation the reed opens and makes a small low pressure area that helps draw in the air. Reverse rotation canl cause the air mass in the crankcase to make a high pressure area under the reed and may cause spitback and reed flutter. Though the Ryoib reed is pertty stiff.
Only one way to know for sure , anybody got a tach and a Ryobi with a CH ingition.?????
RC, G-23s don't count cause they are pistion port.