I'm not sure - maybe it was measurement error on my part, I will double check. Moreover, the EX and EY boxes don't seem to use identical designs, if one believes the schematics drawn on the Pomona boxes. The EY design has a 50ohm input impedance in the stopband, whereas the EX doesn't. Maybe the latter needs a Tee + 50ohm terminator at the input?
Judging by the schematics, the servo inputs to both boxes are driving the non-inverting input of an opamp, so they see high-Z.
I got confused. Why don't we see that too-high-Q pole in the OLTF?