Need the button top and they were designed around the AW IMR 18650 1600mah, I also use the 2000mah. The 1600s can handle a 24 amp draw the 2000s only go to 10 amp the difference is not an issue unless you're going below .5 ohm coils.
flat tops will work but are more likely to have an arcing issue.
flat tops will work but are more likely to have an arcing issue.