The "stub" idea is actually quite a good one.
You publish on CAA G/A charts, it looks very official and intimidating, but in actual fact it means nothing to civilian pilots.
The dimensions usually took into account the parameters of the PAR, (Precsion Radar Approach) or TACAN approach to that runway, both required some degree of lattitude as more than one aircraft could be on final at any one time.
(Add four time ninety four for MOD thinking and you've got the answer
)
I believe that the original concept was to "protect" the final approach of the instrument runway, much as you will see on CAA charts to civilian airports today.
However, as I said, it only indicated a "steer clear" area to military pilots, but only the ATZ applies to civilian avaitors.