The Model X front door edge seems too thin for retractable handles. When closing the door electrically, it can be best to have it open at least halfway, your results may vary.
The following is based on my experience so far and hopefully Tesla Motors will be more specific. They are extremely clear in their warnings to never open both the front and Falcon Wing Doors where the front door is 20 degrees or less. While the DS mentioned the doors could hit, the Owner's Manual only warns that your hands must not be near the front door edge and could be injured if the Falcon Wing Door was to open or close if the front door is less than 20 degrees open.
The Owner's Manual viewed on the touch screen appears NOT provide exterior closing instructions as of 12/31. I have found several ways to close the front door from the outside. The important thing to remember is that these driver/passenger front doors have an electric assist to fully close the door, they do NOT need to be firmly slammed (and IMHO, should NOT be except in emergencies, hopefully Tesla will be more specific.)
The front doors can be quickly but gently pushed from the outside to the closed position from any open position, just check that the front door latches and pulls in.
To slowly close the door, move it to the closed position until it partially latches, the door will pull in and close fully. Any part of the door could be touched, but I would suggest the chrome button to keep fingers from the edge. This would be the preferred method with children or pets, as you can monitor that the door area is clear and free of obstructions.
If you prefer to let the door close electrically using one hand while the front door is in a half opened or full opened position, here are my suggestions with the driver's front door. (The goal is to push the chrome door button without moving the opened door.)
Easiest: If you are standing looking at the outside of the driver's front door while it is in a half or full open position, then with your right hand, then place all four fingers behind the thin door edge and press the center of the chrome button with your thumb without moving the door. Remove your hand away fully as the door electrically closes by itself.
Takes practice: If you are standing looking at the inside of the driver's front door, while it is in a half or full open position, then with the left hand, place your left thumb behind the thin door edge so you can press the center of the chrome button firmly with the left index finger without moving the door. Remove your hand away fully as the door electrically closes by itself. (Vary this method by looking for the chrome button edge for finger placement or feel for the chrome button with all four fingers.)
If there are wind conditions, then the above ideas might not work. Hold onto the door and move it carefully to the closed position and press the center of the chrome button and check that the door pulls in.
To repeat, while these methods make closing the front doors a luxury, do not attempt this unless the doors and your hands are away from the Falcon Wing Doors.
(And if you think my instructions are complex, just wait until you read your Owner's Manual for many additional door instructions and warnings.)