Well, the volume required for the fuel vs. the volume required to house the battery is remarkably similar. They are shaped a bit differently and the battery doesn't get lighter as the flight goes on so you can put it anywhere you want. If I had absolute free choice as to how a big EDF was designed I'd change only a couple of things. The outside shape I'd leave the same, I'd change the internals a bit. Instead of curving the ducting inwards immediately to make room for fuel tanks between the duct and the side at the CG I'd run the ducts straight back along the fuse sides for a foot or so before gently curving inwards to meet the fan mounted towards the rear of the wing. Then the space between the ducts opens up for easy battery access. That space the cylynder head occupied is used for wires and the ESC on one of my setups. There just isn't a lot of empty space inside once you install all the equipment.

Hard to say what's in it since I haven't seen it fly, just heard second hand reports. I've flown two different setups in mine that worked very well, one was appr. 2,600-2,700 watts with a flying weight of 11.5 and one was 2,200-2,300 watts with a flying weigh of 12.25. The 2,200-2,300 watt setup goes a little faster in level flight - it equals the speed in the fastest diving pass in that video but flying basically level ovals. So the fan is better because it is performing a bit better on less power at a heavier weight. Physics is physics, you can't get more than 100% efficiency so if the BVM plane weighs 10 pounds and it isn't doing more than 130 mph it could be as little as 1,800 or 1,900 watts. The motor and battery combo is key in EDF. if they haven't been tinkering for quite a while there is probably room for additional performance but it's all a trade off in power vs. weight vs. duration vs. landing speed and glide angle.