Originally Posted by dddd

To the OP, note that the derailer's upper knuckle swivels on the mounting bolt, but that the stop plate remains in fixed position to the dropout.

So, with the end of the spring "keyed" into the hole in the plastic upper knuckle, you would not want the same end of the spring to in any way "engage" with the stationary stop plate, as this would prevent the spring-loaded pivot from functioning.

So note that, with the parts properly oriented, that the end of the spring will never coincide with the location of the "groove" in the back of the stop plate (that "groove" is I believe some sort of metal-forming trick designed to improve the strength of the bent tab that engages the front edge of the dropout).
It may also be that the end of the spring isn't long enough to actually engage with the "groove" in the back of the stop plate(?).

Sorry non-fixie, I am just now seeing your above post!

Who's on second, anyway?!!