You don't need to see duty cycle unless looking for a fault code. The EHA gives the best view of the adjustment and response to mixture anyway. And there will be no codes if you are in closed loop.
If you had +20ma KOEO then you have nthe right polarity. Your readings indicate slightly lean mixtures with are being controlled in closed loop. This means that is all there is! This does not mean your engine likes it that lean (lambda is exactly as lean as the motor likes it.
Its strange though. If your readings are right, and you are correcting for slightly lean the car shouldn't run better with the EHA removed. If it were slightly richer disconnected that would make more sense.
Bosch Master, ASE Master, L1
33 years MB technician