Whats with the antenna lenght?

[Cedar Mountain Radio]

the sirio vector 4000 is a great antenna if , IF you are in a mild weather area ...

Across town is an op who put up a Vector 4K but first he took large cutters and snipped off the ball on top and put a yellow rubber cap over the top of the rod. He said he had to pull out the aluminum rod 4" more to tune flat but he thought it would help prevent the top from bending in the wind.
He's one of the strongest stations around here and has terrific receive.