I have read that some scientists have data that prove flats yield more than rounds because of "genetic purity."  I don't doubt that but don't know that it's true.  It has been proven that seed shape and placement influences germination which could affect yield.

There are so many variables they are difficult to isolate.  What Leon Bird taught me has held true so I stick with that.

I just want high quality seed.  None of that left over stuff with a little treatment on it that looks like a woman's lipstick worn off.  They won't waste the money the put a heavy polymer and seed treatment on poor seed.

Ed