I haven't used the apex, but from what I can gather from reading and tons of time tweaking it, there is no smoothing option on the xim4.
Take this with a grain of salt, I mean a tiny, tiny grain. This is just me, having some programming knowledge and understanding of aim mechanics giving you my educated guess: I believe that playing with the boost value along with the in-game deadzone would be the equivalent of changing the aim smoothing value on the xim apex.
Sorry I can't offer you more, but I figured since you weren't getting a reply (holidays) I'd give you my assumption