1. ENC is not a controlled function. It activates by default during the call
2. If there is too much disturbance in the close surroundings, then there are chances of disturbance during calling.
3. You need to make sure that they are using the device in the ideal way and MIC is in the right direction as it should be.
 4. For TWS, using 1 earbud or 2 earbuds doesn't impact the calling performance.