[Yes, that is true, but putting LR rubble in your return area does displace the volume of water in that section. So if you have a 5g return section with 2g of evaporation, the water will lower about 1/3. With LR in place, it may lower 1/2 or more which may end up running the pump dry.
Just some food for thought.
I've got the same niagara falls in my new 80g sump, and the return area is very small. I really do hate this sump, but I'm working with it for now until I have time to make a new one.]