They really like CFI's with a military background, specifically mil UPT instructors. Although, about 60% (rough guess) of the DOSS IP's are strictly civilian.
Also the type of instructing you have been doing is important. i.e. someone who has tons of IP time but all instrument or doing BFR's wont get a second look but someone who's IP time is from primary training and is recent will stand a better chance.
About 10-15% of IP's don't make it through the upgrade program.
Cheers,
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