Can someone explain this better? How does the 48" long fixture have more PAR than the 24" long fixture? I'm almost convinced that this was in error by the person testing for PAR, which makes me not believe any of their PAR numbers. If the 48" is just two 24" side by side then the par would be exactly the same. Especially since I was told these fixtures don't use optics like some of the other brands.
look at it this way, each fixture is made up of lots of small lights, and as you said they don't have narrow focus optics - more like a flood light than a spotlight.
If you put one old fashioned incandescent floodlight, say 25 watts, in a dark room and point it at the ceiling it will light up the room dimly. Add a second and the room will be brighter - even if it is pointed at a different part of the ceiling (because they are wide angle floods). Add 30 of these lights and you now have overlapping coverage all over the ceiling - and 800 watts total.
Say the room is very long and you started at the right end. Even as you add more light to the left side of the line of lights the overspill is going to increase the light hitting the right side too, and (jumping back to an aquarium) give more PAR to the right end as well as the left.
In lights that have narrow optics this effect would be much less (more like a line of narrow focused spotlights)