I don't know if this helps, but if you take a portrait with a TLR at 1 to 1.5 metres and place the camera the same height as the subject's head, the fact that the camera's taking lens is several cm lower will mean that you get distortion of the subject's head (in particular, an unnaturally big chin). Is this the effect you are getting? If so, make a conscious effort to position the camera 15 to 20 cm higher.

Regards,

David