If I'm not mistaken, the Highland regiments wore tams that were 12" in diameter from WWI through WWII. I think it's only in the last 50 years or so that the smaller Balmoral has replaced the larger TOS.

Once you get used to the look the Balmoral begins to looked crabbed and as if someone were wearing a child's beret.

I don't know what a contemporary balmoral measures but to these old eyes it never seems to pull over the ear with the grace and finesse of the larger bonnet.

Just my 2¢...