Lange Coupler Input Return Loss Doubt

Dear All,

Please see attached picture for your reference.

Can someone explain me why I get a input return loss at port one (S11) of about -20 dB when provoking a short in the port four (4) while if I short the port three (3) I get only about -6 dB ?

Would not be the case I am supposed to get about -6 dB on either both cases ? So why -20 dB ?


Thanks.