Platform 2/3 at Coventry is ~340m long - but after the last round of refurbishment the usable length is less than 300m. Don't remember there being a 15/16 car stop sign last time I used Coventry (pre-covid of course) think the max is 12 along with other stations on the route.
I'd love there to be a sleeper at Coventry (or even BHM) as it would help with my regular commutes to Scotland but I think paths may be an issue especially if early morning.
If I remember correctly, the sign is past the usable section of the platform. And agreed on a sleeper stop in the West mids. Each time I've used the sleeper I've had to go to Euston first.
Yes it (14/15 car stop) is (in the Down direction) beyond the platform starter signal. Presumably had some custom dispatch arrangements associated with it.