It doesn't though.
If he fires an Enton ball (Of a big enough size) directly at the FRS coming at him, it'll collide with the FRS, consume it, it'll become pure flame and still be on its way to Naruto. The FRS won't hinder the Enton's original trajectory, it'll just be absorbed while the flame continues on its way.
He's not reinforcing Naruto's attack, Wind enhances Fire, not the other way around.
Uh, read that again. All that hit the Juubi was a ball of pure flames. [
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] The shape remained until it hit the Juubi, but it being in a Shuriken shape doesn't mean that the FRS is still intact, cause that only happens if Sasuke matches Naruto's chakra percentage. [
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Lets not bother to mention that they both shot their attacks
toward the Juubi in the first place. Obviously it'll continue in that path. Completely different from him firing Enton at an FRS fired at him.