Just a thought I've had In my head for quite a while: Do you think GLF was influenced by Sid Gordon's book "How to fish from top to bottom".
Gordon describes " the silver bubble" and introduces the Swanson Wet- Dry series of flies which are so compatible with Gary's ESP patterns. I think they were on the same page, Gary and Sid, and Gary was offering up an answer to Sid's question : Who ever solves the kicking legs and the bubble has got it.
"As far down the river as he could see, the trout were rising, making circles on the surface of the water, as though it were starting to rain."- E.H., The Big Two Hearted River