Yup.. it's normal. There is an heating element in your RDA (the wire...) .... So it does get warm. Some rda's will get hotter then others. Design makes a difference.
But without calculating 0.36ohm and 40 watts on the rx 2/3 should be safe. Assuming you are using good batteries.
I'm more of a RTA user then RDA. And some of my tanks for example the aromamizer gets hotter then let's say my bachelor tank. I'm pretty sure it's because of the difference in tank design, so i'm assuming it's the same with RDA's.
Also the aromamizer sits flush on my wismec mod, which means the tank transfers it's heat quite easy to the mod making my mod suspiciously warm/hot. While when i use the tank on.. lets say the cuboid, it doesn't sit flush and hence.. my mod does not get hot..
Design..