To avoid the potential issues you have identified, you should place the mezuzah on the furthest protrusion of the post into the opening and not on the outer tefach. Keep in mind that some authorities assert that one does not need to place mezuzot on the outer tefach of inner doors. 
Placement on other parts of the curve is only acceptable if two conditions are met:
- The whole mezuzah should be within the doorframe and not protruding outside.
- Even though the mezuzah is on the surface of the post, it should not be deeper than a tefach away from the opening.
 Divrei Yetziv Y.D. 191:2.
 Agur B’ohalecha 14:3; Mezuzot Beitecha 289:8.