An interesting thread, Rik. Seems our experiences hold some parallels.
Initially, I modelled in Fn3 scale, as my first loco, an Accucraft Ruby, was advertised as a "Freelance 1/20th scale model based on 3ft gauge Baldwin prototypes". This loco and gauge were chosen based on cost and availability here in Australia, and the much higher number of people running 45mm track, over a mere handful of 32mm lines in the country. My early scratch-built locos and stock were also this scale, but modelling 3ft gauge isn't quite appropriate for a Queensland sugar cane operation, which have always been 2ft.
My first scratch-built loco was based on a 2ft prototype, but the model was "stretched" to 3ft/Fn3, representing a "what-if" 3ft gauge rebuild. The model in the photo below, sitting on the coupling of it's full-scale equivalent, you'll see is proportionally wider than the real thing. (Apologies for the picture size, it was taken from my blog and I've yet to resize the photos on there)
Thus, 3ft was a compromise to suit the Ruby, and the idea was that my line was a rare example of 3ft gauge in Australia. But, as Queensland's mainline railway system is 3'6", I eventually realised that modelling 3ft meant that the locomotives and stock would be hardly any smaller than the "full-size" mainline equipment, next to 1:20th scale figures, buildings and vehicles - hardly appropriate for a cane tramway, their equipment being scarcely larger than Welsh quarry stock.
Funnily enough Rik, I've also changed scales, but have moved in the opposite direction to you.
These days I build everything to 1:19/16mm scale/SM45,
wanting to model 2ft, but still limited to working with 45mm gauge track, as I don't want to lose the track, locos and stock, into which I've already invested so many thousands of hours and dollars.. Although the few 2'6" lines in Australia were never cane tramways, a couple ran through cane country.. So I've settled on using a rubber ruler as well, and calling my line 2ft 6in gauge. This works well enough with the 1:20th loco pictured above, though 16mm scale figures and 1:18 scale road vehicles really help support the illusion, making the trains and their gauge look a little smaller, and closer to 2'6". Maintaining a good quality of finish, high detail and weathering everything, makes an effective distraction from any scale and gauge discrepancies, too.
Whilst we're talking scale, funnily enough, the 16mm Roundhouse locos I have, (Innisfail and Bundaberg Fowlers respectively) aren't actually 16mm scale - they're between 1:19 and 1:20, slightly closer to 1:20 in fact! I know this, as I volunteer at the heritage line with both these locomotives' prototypes, and have measured those locos and compared them to the models. I have a sneaking suspicion the Accucraft Baguley is also this way..
Even so, most of my models are close enough in size and scale, that they don't look out of place in any combination with each other. The only thing that
would have been an exception, was that I did have my cane bins laser-cut to 1:22 scale. Because, as the supposedly 1:19 mock-up shows, they would've absolutely dwarfed everything else. In real life, these 4-ton cane bins look much more like the 1:22 model came out. Go figure.
I do wish I'd have gone for SM32 to begin with, it would've looked a lot better for what I'm trying to do. I'm too deep into 45mm to change now, but with the handy rubber ruler, as long as my freelance operation
looks about right, I for one, am content to call it 2ft6in.