Additional comments from Jim Wild, designer of the de Winton model
To expand on your accompanying notes re prototype and model, the prototype came in varying sizes and basically the small boiler was fitted between straight frames as per Chaloner, on the Leighton Buzzard Railway, and the larger boilers required curved frames as per George Henry in the Tallylyn Museum. (A picture of my coal fired version can be seen below.)
My friend Maurice Cross who built the example covered in the Locomotive of the Month was, and still is ,a professional model engineer. Although much of his work involved the larger stuff, many of the local 16mm Merlins, etc. have been rebuilt and overhauled by Maurice ,and have a new lease of life running better than when they left the factory.
Maurice and I puzzled over your problem of you having to use a blower. ( A blower was never used by either of us and was never required) Both of us agreed that the probable cause was the way the wicks had been splayed out which did not allow enough air to pass the wick.You might like to try a normal wick setup one day. I would be interested to hear if it cures the problem although it might not raise steam so quicklythree minutes does seem mighty quick!
Jim Wild, Reading , England