At least the first couple of carriages are beyond the platform end and beyond the points that give access to the run-around loop, as others have mentioned. The back of the train is somewhere about where I've drawn the red arrow, I think.
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The platform at Aviemore is quite a long one. So it does seem odd that the carriages were sitting in that position, and I would take a punt that they aren't usually, and this will turn out to be a contributing factor.
The Royal Scotsman visits the strathspey railway regularly - so the process of it entering the Strathspey platform from the mainline (ie from the south), and then having a strathspey loco hooked up at the northern end is one that happens often.
This video shows the Royal Scotsman train departing from the Strathspey platform at Aviemore, for a trip along the line last year.
It seems to demonstrate that the RS rake easily fits on the platform, clear of the run-around loop. Obviously something was different on Friday, that meant the coaches were in a different position.