dervish
What was the rationale behind retaining the small scanner in the 3A?
The larger RN radome and scanner, which would have halved the blind arc, was in the original spec approved by MoD(PE). The large scanners for the new Mk3As were sitting in store, brand new, awaiting call forward whenever Westland needed them. Also, the cost of building the 3As with the large radome was slightly less, because it represented the latest build standard.
Mk3 retrofit was also planned, and again the scanners were in place. The cost of changing the radome was about £25k per cab (which would have led to the commonality and efficiency you mentioned).
But the RAF insisted on the more expensive, less capable design.
This extended to the entire radar, because the Mk3A has a hybrid Lightweight Radar / Super Searcher. That is, a mixture of mid-60s and late-80s technology. The RAF spent so much maintaining LWR that the investment appraisal showed a complete Super Searcher fit was more economical. I believe the support costs were in the order of eight times higher. Again, they decided to stick with the expensive, less capable option.
Rationale? Irrational more like.