These initial tests were more about the controlability of the MK910, either as commander or as slave, rather than tests to achieve perfect exposures. I agree spot metering would have been preferable, and maybe I will repeat these tests using spot metering.
If the ambition was to have good exposure of the yellow portion of the flower you would have had to use spot metering with the spot on the brightest part of the yellow. In addition the flashes would probably need some minimum distance from the subject like between three and four feet.
