Geometric filters are different. They don't stay within the boundaries of a single featuretype. The geometric filters are initialized with a geometric object. This is the object that the feature's default geometric object will compare to. But this geometric object can come from any feature in any layer.
This makes the semantics somewhat different as well. We'll demonstrate with a simple example:
Example 6.2. Geometric Filter example
"((x > 190000) OR (FEATURE WITHIN GEOMETRY.1((prov = 4) OR (prov = 5))))"
In this example we see: "GEOMETRY.1(...)". At this point the parser will create a normal filter from what's within the "()" on layer 1. With this filter it will get a FeatureReader and take the union of all geometric objects that are found with this reader. Then it will create a GeomWithinFilter with this geometric object.