If your coils are closer to the edge of the rda deck then the rda itself will get the heat from the coil much faster.
If you chain vape, at least for me, the rda gets hot. The IGO w especially. It isn't as thick of a cap as other rda's so the heat doesn't have far to transfer thus making it hotter faster.
If your coils are firing fine and everything is tight down then what you are experiencing sounds quite normal. If you are really worried then try to build another setup and watch your battery.