HMC346ALC3B application

I have been trying to use the HMC346ALC3B voltage-variable attenuator as part of a laser intensity control circuit, and I am having some trouble with the external op-amp control circuit.

I have wired an external op-amp (AD8675) control circuit together with the HMC346ALC3B eval board, exactly as shown in the datasheet for the attenuator: https://www.analog.com/media/en/technical-documentation/data-sheets/hmc346alc3b.pdf

I am using an external DC power supply for the control voltage. However, I do not see continuously tunable attenuation, but rather 0 attenuation for 0 - 4V control signal and a sudden change to 20 dB attenuation above 4V.

Hoping to get some suggestions about the cause of this problem, or any kind of more detailed explanation / application note for the HMC346ALC3B which would allow me to design a new circuit. Currently it's not very clear to me from the datasheet alone what exactly the V1, V2 and I inputs should be.