The answer about how much you take is both a reflection of what's being stored outside the target's capacity to protect as well as the units you send.

You'll note that with the most recent update, units all got a fourth metric, indicated by a small box icon to the right of their speed stat. This is 'carrying capacity'. One unit can haul away that many units of drugs, weapons, and alcohol from a successful attack, so depending on how many units you send, how many of them survive, and how many 'unprotected' goodies your target has, the amount you'll get back varies.

In general, units that rely more on virtual 'strength' can haul back more loot. It takes four Rowdies to equal the results one Bouncer can net, and two Bouncers to carry what one Bazooka Guy can heft. But generally, the 'stronger' a given unit is, the slower it is to get there in the first place.