There are spoilers about Star Wars: The Last Jedi in this question, be careful.
I first apologize for any wrongly used word or approximation as I am not a particular fan of Star Wars and I have seen each movie once a long time ago except for the last two, which I don't recall entirely.
For my question, it could go the other way as how did Kylo get fooled by an illusion (or clone ?)? From a guy who's pretty far and I'm guessing that's an understatement but have no idea how far.
Since he's a powerful force user I'm guessing he must have some kind of sensitivity to the force, can't he feel that the "force field" around Luke isn't the same? Or even the clone itself, I'm guessing the clone isn't perfect as well(movement speed, reaction time or something) or is it some kind of ultimate technique that draws every bit of strength you have (since we see Luke dissapearing right after)?
And for some clarity about the illusion, we see that Luke avoids being hit so that Kylo doesn't see that it's an illusion. But a few minutes before he touches his sister and even gives her something (the dice thingy that we see dissapearing a few moments later) so he can interact with his environment but only small interaction?