Stuart, you are right about the 'magic catch'. For me personally, it's all right to just enter when uke is moving quite slowly. But if he is rushing towards you... things become tricky... one ends up going behind uke and then struggling with his forward momentum. I guess I'm not skilled enough to control a fast-moving uke without slowing him down... perhaps a forward kokyu nage type throw would be easier
Dario, you are right that blocking doesn't seem to capture the spirit of blending with uke... However, if one looks at Terada Sensei's book (Terada Sensei is supposed to be the highest ranking shihan in the Yoshinkai), tori first stops the shomenuchi... this is not a typical wrist-to-wrist block as in shomeunchi ikkyo omote, but a subtle block (almost only using the fingers) on uke's wrist and elbow. Appreciate your comments though.