First thing: NO PREAMP! You've got tons of signals bombing in, so a preamp will be overloaded and wipe out half of your channels. Do you actually have eight bowtie elements in your design? The picture shows four, which should be plenty.
You may have already done so, but be sure to consult the best site for bowtie array designs
here. There should be a design that will fit the bill if you want to tinker some more.
I think your problem is an avalanche of FM. Try putting an FM trap in the line to see if that helps.