The chipper/shredder distinction has more to do with the input than the output. Most homeowner machines have two inputs. The shredder input is for soft stuff or small stuff (garden refuse, leaves, twigs) and leads to a chamber where the material can bounce around against the blades or flails until it's all processed. The chipper input is for branches, from maybe 3/4" to whatever will fit, and takes the form of a tube that leads directly to the blades.

I've never owned one (only rented), but flail-type machines have screens through which the material passes as it's processed. I believe some of these machines have interchangeable screens that give you some control over the size of the output. I can't tell you how well that works.

As for the reduction ratio, it has to do with the reduction of volume of the material, not the size of the stuff that comes out. For example, if a unit gives a reduction ratio of 10:1, you could expect a cubic foot of leaves to reduce to about three quarts at the output. The exact ratio, obviously, would depend on the nature of the material and how volume was measured at the input.

You might consider renting a representative machine for a day to see whether it does what you want. Or see if you can buy something used on the cheap so you don't lose a lot if you're dissatisfied and have to sell it. Any good chipper/shredder tends to be pretty expensive new.