You want your proxies to be based on the most concrete type of the bean for apparent reasons - you want the proxy to match all possible injection points, so it has to fit into all types, which is exactly what the most specific type will do.

So in your 2 interface scenario with Square and Rectangle, you will always want to base proxy on Square so that the proxy has both types; therefore these methods will return you `Square` - a super interface for the proxy you are doing.