Yep, that's where the cooler will make contact. A tiny dot or thin line on each would work fine. Replace your heatsink...remove to check contact if you want.
BTW...thermal paste shouldn't 'smoke'. Are you sure it wasn't something else? Was it coming from directly underneath those coolers?
It was coming from directly under the heat sink and the only things under the heat sink was the stock thermal compound and some type of foam square around the ION chip.