I am fine tuning my layout design before starting to lay track. I am planning to run 5 coach long trains so need platforms 5 ft long (in OO). I want to put points at the end of a platform for a siding but I am tight for space. If I reduced the platform to just over 4 feet and put points immediately at the end I could have the loco sticking out of the station straddling the points, but is that acceptable pratice in real life. I am assuming that any signal would be in front of points so the train could straddle only if it had a clear road ahead. I accept that this is a model railway and at the end of the day I can do whatever I like but just wondered.
I don't know the rules chapter and verse, but I would reckon that an over-long departing train at a platform which fouled part of the station throat could be accepted as an emergency or very occasional operation, but maybe not as an everyday operation. This would depend on the arrangements at the terminus, but a loco fouling pointwork could lock up a lot of signalling interlocking in the area and effectively stop a large part of the terminus working as long as it sat there. The signal controlling the pointwork could be behind the loco if it was a platform starter and located at the platform end, and I'm not sure about the signalling rules concerning a stationery train straddling two sections.
As a matter of interest, if you are sending out over-long trains, are you also intending receiving them. If so, then you have a basic problem with what you do with the last coach stopped beyond the platform end - or more accurately, what would your passengers do :-) OK, if you are running corridor stock, they could walk down through the train until they got to the platform, but the last coach would probably be a brake end, and anything in the luggage compartment isn't going to go anywhere :-)
You might be better looking at moving your siding turnout, and that might been more complexity in the station throat - which is what happened in real life becasue of space considerations. You might have to look as using something like a slip or a tandem to merge your siding turnout into other pointwork, and let you get you five foot platform.
It happened where I went to school. The distance between the signal and a stretch of single line was insufficient for long trains to clear it completely. That often meant trains bound for the other direction were kept waiting in the passing loop. I wish I had a pound for every gallon of fuel I saw being wasted by trains stuck on that loop.