My tanks that run on a central filter system are all end on, they are small tanks though, just under 300mm in length anyway, I can fit three on a shelf rather than just two, they are for breeding/raising fry, and as Ryan says, not for display.
I use the Hammerlock shelves, my lowest tank is about 400 from the ground - could put some on the bottom shelf, but it would ruin my back and then where would I put my junk?