How to keep baked meringue from shrinking away from pie crust?
Meringue will shrink when it's cooked, there's no way to avoid that.
There are two common options for dealing with that:

A very thick layer, such that as it shrinks, it's still big enough. (Think of the pies that have a two inch thick slab of meringue)
Less connected, more complex shapes, such that as they shrink, they don't all add up to a change that pulls it apart (think of pies with many nicely formed dollups like https://s-media-cache-ak0.pinimg.com/736x/02/d8/43/02d84386535246553b3f4e8463e3047e.jpg )