Cause at 5252 rpm's the rpm and the constant of 5252 in the formula cancels each other out. The cross over has no significance in the power curve of the engine.
If measured in Kw you'll have a different cross over point, you could figure out how much work you can do in a minute and come up Rob power formula Rp which would have a different cross over point but doesn't matter if you use Kw Hp or Rp they will all have the same curve and be mathematically comparable to each other.
