I think that what you want to use it for will work out just fine....keeping away flys and ants in your coop/run. As far as feeding it to your birds..it does say on the packaging, that it doesn't work when wet, which is probably why I have to replenish the run after a hard rain.
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My coop and run dimensions are the same as yours. I sprinkled it around the edges of the coop in April, and haven't done it since. I never see flies in there, but I also clean it every day..easy clean-up because I put trays under their roost. In the run, however, I have done it...