My wife has the Topeak QuickTrack rack system on her bike. She recently bought the Topeak basket that works with the system, however, the geometry of the bike seat and basket are such that she couldn't slide the basket far enough forward to engage the latch without hitting the back of the seat.
My solution? Re-engineer the latch to give some extra space. Here is my model. Perhaps it will be helpful to someone else in a similar situation.
I am working on a Version 2 that includes a little bump on the tongue so the basket can't slide forward while you are riding. Also, the holes are not quite big enough for the screws that come with the "Fixer 6" adapter from Topeak, so Version 2 will also have bigger holes. In the meantime, you can drill them out yourself with a 5/32" bit.