I wish I had a picture to describe this... but I don't. So I'll try to describe it in words...
I've seen a unique entry pipe on a Hershel House rifle. From pictures, it appears he used it on other rifles and pistols. The pipe is formed in 2 parts. The pipe portion is made the same as the forward pipes would typically be made (formed round from sheet). The rear extension is not formed to fit the contours of the stock transition from upper to lower forearm in any way. It's basically a flat plate that is riveted and soldered onto the round pipe to form the rear extension. The share of the sides is an elongated teardrop, but it's still a flat plate.
I think I've seen a picture of an original gun (possibly a pistol) that used this same kind of entry pipe, but I can't remember where. I'd like to know if any original gunmaker used this style, what school/location/time period, and if anyone else was using it within the school. Pictures of original guns would be great too.