LNER don't like having multiple stopping positions so generally the 5 cars use the same stopping positions as the longer trains. Hence at Grantham you see Hull Trains 802s with 2 stopping positions for 5 and 10 cars but the LNER sets use the same ones. Customer unfriendly but negates the risk of a stop short I guess which if it causes a cancellation is even less friendly.
Yes, as above, it is mitigation for a stop short door release incident - Driver releases doors on Azumas, and LNER have a multitude of different train lengths compared to other operators.
Why are thameslink trains unable to use the same stop markers as other services?
As below...
At stations with signals at the platform ends, there are signal sighting issues because the driver sits in the middle of a class 700 but to one side in a class 379 or class 387.
And also...
A central driving position (so signal sighting will be different), and
tiny side windows in the cab door meaning they can't be used to view stop car markers - 700 stop car markers are lined up against the edge of the windscreen.
I'm pretty certain that when they were introduced the Azumas had different stopping points, depending on whether they were 9/10-car or 5 car. I can't comment on the operational side of things but it was much more passenger friendly. As mentioned above there is now the situation where the 5-car trains stop at the far end of the platform, where there is no cover from the elements which means people end up running. Of course we now have 5-car Azumas stopping in different positions to 5-car Lumo trains for added passenger confusion....
The 700 stopping boards is also interesting. There were separate boards for 8-car and 12-cars when first introduced, which again was much more passenger friendly and helped to spread loads throughout the train rather than concentrate it in the rear couple of cars if an 8-car turns up. A couple of years ago the 8-car stopping board was removed and all 700s now stop at the 12-car board. Again, as mentioned above, 8-car 387s (and 365s before them) stop at a much more passenger friendly stopping position, which is different from the 12-car position.
It's not a platform camera or monitor thing at Stevenage because there aren't any, so I really don't know why it is.
387/379 boards at SVG cannot be moved due to wheelchair ramps being obstructed by platform buildings/furniture if they go right down to the ends like the 700s.
At St Neots there are separate RLU (Reuced Length Unit - 8 cars), and FLU (Full Length Unit - 12 cars) stop car markers for this reason. 8 and 12 car 387/379 in the Up direction stop at the end (but RLU stops midway for the wheelchair ramp!).
It's not just signal sighting, method of dispatch, platform curvature and possible large gaps between train and platform, platforn lighting - but also risk of slips trips and falls from passengers running for trains if the stopping position is far from the entrance to the platform.
Drivers would like all the stopping positions to be at the end, and passengers nearest the entrance.
But it isn't very simple. One reason for differering stopping positions on different types of train is that, as an example, 387/379s have bodyside cameras that face backwards on the driver's side (left) of the train, and forwards on the right hand side. 700s/717s face forwards on the left hand side, and backwards on the right hand side. This would work for moving the RLU to an ALL board on the Up Slow at Stevenage as the one board for any length 700 mitigates stop short door release incidents, but means people running for the train can be easily seen. 387s cameras face the other way, and rarely run as 12 cars stopping there, so the stopping position for 8 cars remains in the traditional 8 car spot, with a clear view with cameras of passengers arriving onto the platform and not having to move along it.
It's a minefield! Keeps the safety section busy with risk assessments though i dare say!