Nope. Reducing the port won't let you get the same volume of air though it. There are limits to how much air can flow through a given pipe diameter. Maximum 400CFM/680Mper hour for 4"/100mm pipe and about triple that for a 6"/150mm pipe. Because a DCs high volume low pressure system only has a few inches of pressure difference the atmosphere can only push so much through so the volume drops off when you go smaller. All that Bernoulli stuff in school that I thought I would never need.
So if you want better dust collection, especially the fine dust, you need bigger ducting and that usually requires opening up the outlet port of the machine and in many cases opening it up 2 to 3 times the area on the other end to let air in to be drawn out. You can't improve collection if you close off the holes and slots in a cabinet. Suck on a straw with your finger over the end and see. No air in means no air out.
I just got up and need to have a shower.
Pete