Some time ago I found an interesting illustration of a "long" Mandylion. First in the Holger Kersten&Elmar Gruber book "Jezus ofiarą spisku" (the polish edition of The Jesus Conspiracy) I provide a scan from it [Illustration1]. The picture is not adressed anywhere in the book, and as the source is given simply "Bibliothéque Nationale". The same picture is reproduced in Antonio Teseo blog, who gives the source as Bibliothéque Nationale, ms lat.2688, dated 1280-85.
Another time when I saw this illustration is in Francesac Saracino 2007 documentary LaSacra Sindone; la storia. [Illustration2]. It confirmed that the illustration is generally monochromatic. However it is certain that the cloth is "long" (just look on the position of hands and the frame [Illustration3]), even though nothing more except the face is seen on it. It shows that the cloth have been considered by some as much larger than often claimed, larger than just handkerchief. Possibly large enough to contain the image of the whole body (as implied by Codex Vossianus and Ordericus Vitalis), even though, as I said, only face is depicted on the presented illustration.