Well, when I simply put it on a plane (or a sphere or whatever), the reflection on the ground is still hardly pixelated when it get to a certain distance. So I don’t see how an other object to have my HDRI image will change anything (or don’t really know how to do it), I think the problem is just on the resolution of the reflection actually 
(I’m still new to Unreal so I don’t fully aknowledge the limitation of it)