Alnico lenght to pole surface ratio

[Down Time]

I've been reading some magnet manufacturers websites. Most claim to ensure good magnetic performance for alnico 5 the length to pole surface ratio should be 4:1. If an standard single coil alnico magnet is .195 then it should be .780 L. The Jazzmaster pickup magnet spec is .195 by .471 L. The B string on a vintage staggered Strat pickup .630 L. Will they start to demagnetize themselves if they are under this 4:1 spec? What gives?

[David King]

We've talked about this, some pickups are designed with a "keeper" structure but the fact remains that over time alnicos will loose some of their charge.
I don't think Leo or Seth et al lost much sleep over it.