I'm not really sure what benefit it would be to run the HMF foam diagonally across the sump versus the traditional way. It would probably work just fine but seems a waste of space that might be used more efficiently.
If you are looking to improve the debris trapping ability of the sump, you could use the traditional narrow dimension installation method but use a combination of different pore size HMF's to trap debris.
I can't draw even a simple diagram as yours (very nice, BTW) but you could use a coarse (10PPI) mat that was installed 4" from one end of the tank that filters your incoming water from the aquarium. Next 'stage' could be a 20PPI mat and if you wanted, add a 3rd 30PPI mat. The heater could be placed in the same section as the return pump.
The progressively finer PPI mats wouldn't have to span from the sump top to bottom if you were concerned they might plug up and overflow the sump. Here is a link to Swiss Tropicals basic WET SUMP
Eheim Pimpette #270
Eheim Pro II 2028; Classics Series -2215, 2217, 2260, 2262; Pro 2229 Wet/Dry