Hi Steve,
Welcome to the IIS forum and thank you for your comments... yes I have access to Agilent E5061B here at work, and will certainly try your method at first occasion
My conclusion after playing with this filter (4 resonators) at home (I have SA with tracking gen and reflectormeter bridge) was coupling was too high
In the meantime I build another one (3 resonators, 10MHz,
see here).
Interestingly, this one has too low coupling, and losses are also too high.
I even used copper sticky tape inside but the result is still not good enough for my taste.
Next I will try with thicker rods, they are easy to replace.