The tree he used his 28" bar on can be cut with a 16, 18, 20". Set the face (gob, angle, wedge), bore the centre of the hinge out from the front through the face, fan it a bit, bore in each side behind the hinge, set the hinge, leave some holding wood at the rear. Take the saw out and trip the tree with an angle cut from the top down towards the rear of the bore cuts...Bang over it goes. In Euroland the final trip cut is called a 'dogstooth'.
Set wedges if you feel you need to.
The shorter the bar, the more important it is to remove the root flares.