Xu Wenfung wrote:
... I just cannot fathom any other method of ukemi other than back fall.
I don't know if this helps, but I always believe that there is not that much difference with sumi otoshi. Being thrown with tenchi nage, one can hold on to the "earth" hand and take a forward breakfall just as one could do with e.g. katate dori sumi otoshi, holding on to the hand that was grapped in the initial attack, the only difference being that nage's second arm happens to be in a different place.