It's hard to determine the exact location because I was dropped off by the boatman almost in the middle of nowhere. But my guess would be the location is somewhere between Panglima Reef and Lobster Wall. You can see Sipadan-Mabul Dive Resort (SMART) from here.
A rather misnomer because I did not see any lobster nor any real reef. But there was a substantial drop-off at the edge of the shallow area, marking the end the of the "reef" area.
The main attraction here is it's shallow water! You can swim with your hands touching the ground - making photography a great experience! While you do not see a lot of swimming fish, but the variety of smaller corals and colorful seaweeds made up for it.
Throughout my snorkel, I saw saucer leaf algae (Tubinaria species), finger leather coral (Sinularia species) with a bright orange ascidians (Polycarpa aurata) on it, mushroom leather coral (Sarcophyton species, often mistaken as a budding sea anemone), brown sea whips (Menella species), and some variety of fishes, if not much.
And it was here I practiced my underwater "macro" shot due to my ability to hold my hand stable without any noticeable current. The results were great. To me, the underwater life in Mabul does offer different theme as compared to Sipadan.