Amps might be part of it...but if you look at the FR graph for the Atticus, it rolls off under 100 hz a decent amount.
https://www.innerfidelity.com/images/ZMFAtticus.pdf
Eikon, on the other hand, doesn't roll off.
https://www.innerfidelity.com/images/ZMFEikon.pdf
HP-3 doesn't super drop until about 30 hz, but it's not really noticable and can hit a 20hz tone with no problem.
The Atticus definitely capable of some thumping, especially in the upper mid-bass area. But to use an example, look at "Vacacion" by Nelly Furtado. The beat has a good sub bass rumble/thump that pounds hard on the HP-3 but only kind of grazes on the Atticus. On the other hand, "Attention" by Charlie Puth the bass beat (which is definitely higher than Vacacion) hits a bit harder and tighter on the Atticus.
They're really two different headphones that emphasize two different areas of the bass. I'm kind of surprised the HP-3 can hit as hard as it does considering how (semi) open it is. To me, the Atticus was made for "real" instruments in mind. Snare drums, acoustic guitars, vocals...all sound so good. But if you like thwomping bass with clarity and you choose "EDMLORD" as your user name...HP-3 I would have to recommend.