That strikes me as a bit of an odd thing to do, what evidence was there that the wheelpit tail goit was feeding into the shaft?
If the shaft was for pumping I'd be more inclined to say it was an outlet level for the water being pumped up, while if it was a combined winding/climbing shaft my money would be on the footway starting at the level, in a variant of the common Derbyshire practice of having a short climbing shaft adjacent to the engine shaft but linking in to it 30-50ft down.
Also, as EH have given it an award I presume there's a archaeological write-up for this work, is it in the public domain or will it be?
Follow the horses, Johnny my laddie, follow the horses canny lad-oh!