How to auto direct call to Bluetooth (Rather than selecting everytime)

Scenario 1: when AirPods is connected to my Mac and I get a phone call

Situation: I pick it up from Mac and can attend call on my AirPods, perfect.

Scenario 2: when AirPods is connected to my iPhone and I get a phone call

Situation: I pick it up from iPhone but I had to select AirPods every time manually. which is irritating as I have to pick my phone, select the AirPods even though AirPods are already present on my ears

so I searched and found this discussion thread: (How to auto direct call to Bluetooth (Rather than selecting everytime)

https://discussions.apple.com/thread/2757804

but when I followed this setting it break the ideal scenario 1 mentioned above.

let me explain how

New Scenario 1: when AirPods is connected to my Mac and I get a phone call

New Situation: I pick it up from Mac but this time the AirPod unpairs itself from Mac and connects to my iPhone. this should not happen because this time I intentionally want to use Mac and AirPod to pick up a call

Any ideas anyone?