My guess.... based on experience of researching UK infantry doctrine, is that they "sort of made it up as they went along."
The UK tends to apply their own manuals to this sort of problem. So take PAM 45 as adapt it to the local bods, whoever they may be.
I very much doubt if their are any specific manuals relating to this area, but I could be wrong. Brits writing useful stuff down is, sadly, pretty rare.
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