The key to using a Geddes style "filler" sub of less capacity is that it is set to a level that is a fraction of the 1st two sub locations. Of course these will not keep up with Tumults if they are asked to do the same duty.
The reason for using this smaller, lower output sub are twofold. First, most people are limited in space towards the back of the room and can't afford to have mammoth subs back there. Second, you can have imaging issues if you run the rear filler sub at a level equal to the front subs.
The reality is that with a highpass around 30hz and running at least 8-12db lower than your Tumults, these subs should be fine unless you are running maybe 10-20db over ref.
Your setup is less than ideal IMO. I would prefer that you separate your Tumults into two separate locations and colocate the Daytons and find a single location in the back of the room. I'm sure you can make it work well as it is though.
Frankly, IMO, the Geddes approach is practically superior to Welti/Devantier. I'd guess that Geddes utilized Welti's research and the approaches certainly work on similar principles, but the Geddes approach is more flexible and reasonably executed. For the Welti approach you basically need the same capacity in each sub location and some symmetry. You built more towards the Geddes approach, but implemented the Welti approach.