I did a Technical Request to Airbus a few months back regarding this.
XXX: My name,
ZZZ, ICAO Code of the airline I did the request for.
Dear XXX,
The following is in response to your message that is outlined below:
QUESTION:
We would like clarification on the recommended feet position during taxi, takeoff and landing.
FCTM
PR-NP-SOP 70 P1/2 gives us informations but the wording is not very clear. Should the feet be on the rudder pedals or heels to the ground ?
ANSWER:
Airbus would like to inform ZZZ that as mentioned in ZZZ A320 Family FCTM
PR-NP-SOP-70, the feet position has to ensure full rudder deflection combined with full braking, even in differential, can be applied instinctively and without delay.
As long as the above combined actions are met. Airbus does not have any specific recommendation on the where feet position should be.
We hope this satisfactorily responds to your request and we remain available for any additional information and assistance.
Best regards,