I'm very sleepy, so this may not be english. Sorry ;-)
So, you have heat problems. You think heat sinks are going to help. You don't know which ones to get because, well, the E16's haven't been out long enough for after market parts.
No worries, this is a simple problem.
There are a number of heatsinks for 380 sized heli motors already. There are many out there and they all follow the same basic formula. These sinks wrap aound the WHOLE can. That won't work for us because the fins interfere with the chassis, the receiver, the slipper nut, and the ESC. How do we fix this?
So the formula is basic. The heatsink NEEDS to cover more that a 180 degree arc's circumference of the motor. This is simply because the sink needs to be press fit to the motor. If the sink covers less than a 180 degree arc of the circumference of the motor, then it will simply fall off.
So, buy a sink. Mark off a 200-210 degree arc of the circumference of the sink.
We could stop here and simply make the cut and snap it on. Optionally, one might endeavor to eek out more material from the original sink to make as much contact with the motor's surface area as possible. At this point, the rest should be fairly obvious. Find out how much sink you can leave on until you have interference, trim:
Then press fit it on to your ride:
For passively cooled applications, you want thick, short, widely spaced fins. This means low surface area, which is bad, but unless you force air through the fins, thin, tight, tall fins will trap air and become useless. Even the cheapo sink I'm using doubles the surface area of the motor, and what more important, that surface area is on top where there is actual airflow.
Computer CPU thermal contact paste could be used to assure that there is full contact with between the sink and the can. It's just a little messy and using too much is simply waste.