Those two spars are long, and extend beyond the kite itself , with one end a ferrule and the other an extension to push into the ferrule to connect the cells. The cell itself has a spine of 55cm, a spreader of 72cm with a leading edge of 45cm and a trailing edge of 61cm. I bought the first 4 cell unit and it didn't fly very well, so I had to buy 12 more for a total of 16 to get a good stable kite. If you really want to be different you can produce a composite structure using both a structural arrangement of cells, AND changes to the individual tetrahedral cells. Making a different change to each individual cell in a tetra can lead to some very interesting a weird designs.
Tetras can become very un-tetrahedral in style, though still being based on that cellular design.
In fact by some small changes you can also remove much of the heavy sparing normally required for a tetra. In fact it is braced in a simular way to a Tri-D Box, which greatly reduces overall weight of the kite from a typical tetra of that size. This kite on the other hand was rock steady, flying all day on a light sea breeze in the morning, until the rear two cross spar dowels broke when the wind became very strong. In particular note the kite in frame 5. Frame 8 shows the same kite again but with the upper 4 cells having the extra long spreader, instead of the lower cells.