you are right there is no kick... And I always thought he nudged him off like pushed him...

there is something that could be better than in the original sequence. Because Luke is totally obscured on the shot of Vader falling back. What if Luke's lightsabre actually was connecting with Vaders when he raises it up before he falls. And the sound of them connecting. Just an idea to perhaps make it more dramatic. Like Luke pushed him off with the light sabres connecting and not a hit and Vader stepping back into nothing.