If I understand synergy correctly you cannot get a +4 on NQ feet. You'll need to get the +1 for that. Also I think it requires a HQ3 to even be available. If anyone has more accurate info, feel free to correct me.
When you pointed out it was a NQ I thought that as well, but I just did a quick search on BGWiki, the source I usually go to for sky augments, and it says both feet can receive 4%. I'm not sure though and someone should confirm if it can or not.