That screenshot appears to be from PhysX Visual Debugger, right? Unfortunately, PVD does not render the ‘inflated’ size of the controller capsule, with the contact offset taken into account. Therefore, no matter what size you make the contact offset, PVD will always make the shape appear slightly smaller. The docs caution you to add the contact offset padding to your rendering visualization:
A small skin is maintained around the character’s volume, to avoid numerical issues that would otherwise happen if we let it touch other shapes. The size of this skin is user-defined. If you render the character’s volume for debug purpose, remember to expand the volume by the size of this skin to get accurate debug visualization. This skin is defined in PxControllerDesc::contactOffset and later available through the PxController::getContactOffset() function.