shihonage

I think it your response (or initiation as some might say) movement should be done with intent on reaching uke's face. Its not entirely a block. You let his strike slide under yours a little, as your hand goes toward his face.
It's not about STOPPING him (and not about hitting him in the face) but breaking the intent of attack (feel as if youre the one attacking, not him! he should feel your intent, not vice versa !) and give you time to step in.
However your "block" should also introduce some pressure on his arm.
You "ride around his resistance" as you move to his side and let him through... the passive/active nuances vary depending on the size of the opponent and the strength of attack.

...or, I could be entirely wrong.