The railway constraint was because of British railways and the need to transport tanks from the factories in the home country - not across Europe.
I keep saying that all the time - the wide Medium Mk.II was transported across the UK by British railways.
The fighting compartment refers to the area the crew uses which includes the turret but in the British design did not "flow over" the tops of the tracks
as in have sponsoons as the T34 and Panther. This kept the hull height down.
Matilda II, the best British tank before the Churchill was debugged, have had the sponsoons. Hull of the Matilda I was much higher than the returning tracks.
The British may have had many designs but again most were not able to be refined due to budget constraints.
In many instances it is not easy to make a silk purse from sow's ear.