I don't treat my inbox as a NA-box. The items in it only become (attached to) a NA after I process my inbox. I take an item out of it and define a NA for it. So if I would see things that need to be processed together I create a NA that processes these things together. If this NA, the processing of all these things together, can be done in 2 minutes, I'll do it. Else it is written on the NA list.
I do a NA if I can do it in 2 minutes. But there's only a NA after I've taken out an item and decided what the NA should be.
Hope this makes sense.