On a 'Conventional' ;locomotive it clearly makes sense to locate the cylinders at the front under the smokebox to minimize the distance to the blast pipe. On 'Fireless' loco's cylinders are often under the cab as there is no blast pipe & this makes for a more direct steam circuit. So, why om most Garretts are the cylinders at the outer not inner ends, some German Mallett Tank Loco's have cylinders in the middle. In the same way while it isnt without problems why not place the cylinders on a SAR Class 25 Condensing loco at the rear not the front of the loco. All these would result in shorter steam/exhaust circuits.