Gents, can anyone authoritatively say how the numbered boilers were laid out in British cruisers (of WWII), and more specifically in HMS Exeter?

In Exeter each of the two Boiler Rooms had four (4) boilers, two either side of the centerline, and were numbered as A1, A2, A3 and A4 in ‘A’ Boiler Room and B1, B2, B3 and B4 in ‘B’ Boiler Room. That is, two to Stbd of centerline (in each BR), and two to Port of centerline (in each BR). But which boiler was which number?

Remember, key word above is "authoritatively".

TIA.