Consider the following two Groovy classes:

package test6

class Foo {
  URL doSomething(String s, URL u) {
  }
  
  URL doSomething(Integer i, URL u) {
  }
}

And:

package test6

class Test6 {
	
	Foo foo = new Foo()
	
	void bar() {
		URL u = new URL('www.example.com')
		foo.doSomething('ciao', u)
	}
}

As you can see with F2 or F3 over the call of doSomething() on foo, Greclipse correctly detects that the call references Foo.doSomething(String, URL). However, if you put the cursor over Foo.doSomething(Integer, URL) and you press Ctrl+Alt+H (Call Hierarchy), you'll see that a reference from Test6.bar() is detected, which is not the case indeed.