There's some debate about how distance from the strings related to changes in tone: whether the distance itself has an effect, or if the difference in sound is due simply to strength of magnetism reducing as distance increases. Those who judge based on the principles of physics tend to believe field strength is the only relevant factor. Myself, I'm not entirely convinced of that. I feel the shape of the field also matters quite a bit.
It does seem to me that stronger magnetism might be useful in a situation like this, where a lot of distance is required.
I think a (smallish) neo bar underneath might be the answer for such a pickup, a really strong magnet perhaps allowing lighter wind and tighter coil(s).
Then again - especially in a neck position pickup - there's the extra string pull to consider.
I imagine several options were tried before the Secret Agent design was finalized.