Rank and drop rate
Minions can drop them but you will get a better drop rate per kill with bosses.
ParagonWiki to the rescue - again.
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In short, a LT has twice the chance of dropping a recipe that a minion does, and a boss has three times the chance. This is why people refer to drop rates in "drops per minion-equivalent".
So lately I've been farming +0/x8 missions solo in an effort to hopefully snag some purple IOs, and I'm trying to find the most efficient way to go about it. What is comes down to is whether or not Bosses have a greater chance of dropping rare/very rare recipies (or salvage for that matter). Can minions even drop purples? What's more efficient, +0/x8 with or without bosses?
The off-beat space pirate...Capt. Stormrider (50+3 Elec/Storm Science Corruptor)
The mysterious Djinn...Emerald Dervish (50+1 DB/DA Magic Stalker)
The psychotic inventor...Dollmaster (50 Bot/FF Tech Mastermind)
Virtue Forever.