is there a reason for using the same fuel % from break in to flying ?  when changing % can change flight times?

  I use the same fuel, because that's what I have. I see no reason to change fuels for "break-in". When you change fuel, oil type or content in particular, it takes many flights before you get the full effect, maybe a gallon's worth at times.

    Changing either the nitro or the oil percentage changes the flight times. Less nitro runs longer, more nitro runs shorter. More oil displaces some methanol/nitro so it runs shorter for a particular volume.

    Of course the engine tends to run longer when the air is thinner, like when it is hot outside, or at higher altitudes, because you lose power. I correct that by varying the nitro to get about the same flight time as my "baseline", if you do that, the power is about the same, the run time is about the same, and the engine works about like it always does.

   Brett