Port placement isn't usually an issue, unless of course there are relatively low-frequency standing waves within the cabinet that cannot be attenuated with stuffing. In that case, port and driver placement become important because response is affected by the standing wave nodes and how they line up in the cabinet.

Tower cabinets longer than a couple feet are the ones I'd be mostly concerned with because they can act like transmission lines. That's fine if that's what you're designing, otherwise, at least be aware of their influence. In smaller cabinets, the port position doesn't matter too much, it is purely a Helmholtz resonator.