Jarvy
For the size constraints, see para #1.
Design
Re the internal design, see the last para in the first section of this
AEC Magazine - Heathrow Terminal 5:
There is no need to say sorry, I was only giving your some information and I hope that it is interesting for you; I know a little more than most about some aspects of T5, which is perhaps partly why it disappoints me, as it could have been world class and the failings are by and large a series of small things.
Also, some of these things probably only effect premium travellers, so I suppose if I was flying economy I might find the place a better experience, if that makes any sense.
One thing I do like about T5 is the selection of restaurants and in particular Giraffe, which feels like a restaurant in a big shopping centre (i.e. better than the usual airport experience.)