*ponder* hmm.. would it really?...
(I'm not sure at all about this, but hey, I have to ask to get answers

)
A traditional dual pelt plate/block would look like the left part of the pic. Let's assume that a plate like that is say 6 mm thick.
On the right pic i've added two halves of a traditional block behind the triangle (the size isn't exact there on the triangle) The base of the triangle has to be a bit thicker than (2x(traditional block height)) due to core size, but there would still be less mass to cool in the triangle than the traditional block, and the distances from the core to the outmost parts of TEC's are about the same on both blocks...
Height of the triblock is slightly less than a pelt's width due to the slanted mounting, let's say i use 50mm pelts, and the triangle has a 20 mm wide base, while the traditional plate is 6 mm thick...
trad. block: 100 x 50 x 6 = 30'000 mm3
triblock: (~50 x 50 x 20)/2 = ~25'000 mm3