Hmmmm
in comparing a maps on where the Tbolts were vs. where the Whelen's are.
We had ALOT more T-bolts before, than we have Whelen's now.
The T-bolts were nested so each siren was within the effective range of the next one in line. So that, if a T-bolt malfunctioned, it's surrounding sirens kept it's area covered.
The Whelen's on the other hand, are spread out widely. there trying to cover most area possible with the fewest sirens possible. the effective range ring of the next siren, starts where the next one ends, an there is a diamond shaped coverage gap in the center in between where 4 sirens are placed.
An since there so widely spaced apart, if a siren malfunctions, it's neighboring sirens can't cover for it. leaving another larger gap in coverage.