Why is it easier to make a confident stroke over a 20-footer than it is over a four-footer? It all comes down to expectations and fear. With little of either attached to longer putts, mental roadblocks are much less intrusive.
In order to bypass the inherent mental obstacles that accompany shorter putts, attach the stress-free nature of a tap-in and transfer that mindset to those middle-length putts.
Using an old hole, the confidence that comes from knocking those putts right in the middle can be transferred to the nervy four-footers.