[Antennas] top hat for vertical

[fkamp at comcast.net]

I have a little query that someone with more experience might be able to
answer and save me some time.

I am putting up a vertical to cover, mainly, 30 meters.  Got about 26
feet of aluminum tubing.  I intend to mount it on the roof, base about
20 feet above ground level.  I will be using open wire line and four
radials so I can use it on other frequencies with a tuner.

I can put it up as a self supporting structure but the winds here can be
pretty strong.  I doubt it would survive one season being self
supported.

I am planning on guying it at its 13 foot level.

I can guy it with insulated line, or I can use a set of wires to act as
a top hat at the guying point.

Most top hats I have seen are installed at the top of the vertical, but
that is not the optimum guying location.

So I am wondering how effective a 'top hat' would be if it is located
half way up the vertical.  Any loading that will allow me to reduce the
height of the vertical would be welcome.  I just dont have a feel for
how much height I can sacrifice with a 'top hat' located at the center
of the antenna.

Any suggestions?

Regards,
Frank Kamp
K5DKZ