The bonnet doesn't show well in the picture, but think of a balmoral with an extra long front that flops forward, worn without being pulled to either the right or the left side of the head.
Similar to how the Khaki TOS is worn. Of course I can't find a ruddy picture online, but I'm looking at a photo on the front cover of Ted Nevill's The Scottish Regiments (Europa Militaria No. 24) that shows a KOSB Drum Major wearing a Kilmarnock/Atholl being worn in the fashion you describe. There are quite a few photos inside of Khaki TOSs worn that way as well.

I have a Royal Scots TOS that was given to me by an expat who served with them, btw.

T.