LPF->BPF transform, strange result

Hello,

To transform a LPF to BPF, the following frequency transform is made:

ω=(1/w) ( (f/f0) - (f0/f) )

ω is related to the generic LPF prototype filter, so ωc = 1.
For the BPF with a bandwidth f1...f2:
w is the fractional bandwidth: w=(f2-f1)/f0.

Suposing a zero is added at ωz, what is the corect resulting fz for the BPF?
Solving the transform equation gives two fz values, negative and positive.

E.g.:

w=0.05
f0=2GHz
ωz=2

Gives: fz= -1902MHz or fz=2102MHz

Which one is correct?
In an EM simulation of the filter I got fz=2106MHz, and in a lumped component linear circuit simulation I have fz=1904MHz.

Thanks