When the Horwich Crabs were being designed, George Hughes ordered a suitable tender, based on the later ones attached to the Dreadnoughts, to go with them. Needless to say, these would have matched the width of the cab. Henry Fowler, on taking the CME's position late in the engines' design process, ordered that they be paired with the LMS Standard 3,500 gallon type, derived from the Midland article.
The Horwich and Stanier Crabs often receive criticism for the mismatch between their cab sidesheets and tender sides, but they weren't alone. When built, the Royal Scots also got this tender, as did the early Jubilees (some of which had them very late on), although some of the 5Xs managed to dump them on to 8Fs, which therefore also share the ignominy.