The induction side (as is the exhaust, if we're really honest) is a MIGHTY complicated thing, you can break it down to a few common variables that affect the fill grade of a cylinder, one of which you've already pointed out:
1) port size - bigger ports obviously flow more fuel
2) port length - just imagine a wave (tsunami) being sucked into said port and bouncing off the valve and bouncing back from the back of the airbox, the carb slide and other obstructions. Now if the length is *just* right and the wave is moving towards the inlet valve, whilst air-petrol-mix is sucked in, you can actually get more fuel in than what you'd suck in regularly
3) valve size to port size - there's quite a bit of literature and depending on what you use the bike for the valve size will be somewhere from 50-60% (stationary engines like generators) to 85-90% (high-rpm-only race engines) compared to the port size
4) cam-characteristics: Not only does the size of the valve and point matter (they limit the max flow at a given time) but also how far (cam-lift) and how long (cam-duration) they are open. Add overlap (when both inlet and exhaust valve are held open), which will promote scavenging and improve the fill grade of the cylinder, eventually at the price of worsened fuel economy.
I won't go into cam specs as that would completely go beyond the scale of the question, suffice to say, you can't infinitely prolong the duration (prolonging the duration will at a point for example adversely affect the idle and low-end characteristics) or lift (the valves will either hit each other or the piston or both).
That being said, it is quite reasonable to assume, that a Ducati 160 sports a cam with a lot more lift and duration (lift affects the fill grade by the 2nd power, as it's the surface of the gap opening up), so with a bit more lift you can have tremendous amounts of improved flow, if the port is large enough. Assuming that both engines will (roughly) rev to the same RPM, the Ducati will also sport a bit more duration on the cam.
With those informations, you can quite easily see, why for example base aftermarket cams for US-V8s usually sport a bit more lift and a touch more duration (if any at all) and still you can often get quite impressive gains, without any accompanying mods.
Hope this helps
Greg