Can you turn off/disable a component after AD9361 Tx output? Do you have a switch that you can use to break the signal path to the antenna?
It is not recommended to change the attenuator setting. Increasing the attenuation would reduce the signal level and at some point will prevent the algorithm from converging. Some small amount of attenuation may be fine, but it sounds like you would need to attenuate the signal by a lot.