re: significance of mid-run reduction in flight ratio
I saw a similar drop to ~1% on the right foot record at about 6 mi into a 10 mi training run. It correlated to a tightening of my right calf which I could not shake, and actually the signature in the record preceded the point in the run when I first noticed the feeling. I reasoned that I was favoring the right leg. (It did get sore later, left did not)
re: sensor flopping around
At that point I began to experiment with L & R comparison more seriously, and I started taping the rS units down on my laces. Standard is a full 360 wrap, sole and all, with 2in wide 'paper tape' (the type used for holding medical bandages on delicate old skin, being easily removable. It's in drugstores). This did change my typical readings, more the pronations than the flight times. But the point is it noticeably changed things and at least for close comparisons I think it is best to do this.
re: flight time
During a period when the right foot regularly read flight time 1% to 2% below left foot I went out and ran 400m (slow) giving myself the cue to accentuate the launch & hip extension on the right side while keeping a weak launch on the left (harder than it sounds!). The rS record showed the R flight ratio to be 2% higher than the L.
re: flight time definition
The above experiment would indicate (but not prove) that Right flight ratio might be % of total stride time (L+R) spent in the air (both feet off the ground) after the right foot ground time. This would require that the pods communicate with each other to establish a common time base and I am not sure that they do that.
Bottom line: flight time balance is a sensitive indicator of when you are favoring one leg for any reason. best to take time to self assess if it shows a change.