why cant you put a small port weapon in a large port ?

I guess it's sort of like trying to plug a male mini-USB connector into a female regular USB port.

It'd rattle around a lot and come loose while you're flying. Bad Idea(TM)

+1 to abortretryfail's response

maybe they could make large port/small port adapters : p

I thought of suggesting adapters but I think it raises a few balance issues. For starters things like sunflares are actually pretty imbalanced when you consider their large port equivalents, in many situations is it preferable to have a sunnie to a jack for weight ratio reasons so you'd have triflare centaurs or dual neut/flare centaurs which has issues.

Then theres the fact that you have the megaposi, which in most circumstances really acts like an adapter anyway, its light weapon that packs heaps of punch, way more than its small port equivalent, so why use anything else?

It's a good idea as an easy fix to add some variation perhaps, but I don't see it happening due to all the combat model conservatives and/or incarnate logic.