I can't help with that, but I'll throw this out there...when I was there a couple decades ago on a dive trip with my brother in law, diving with some dive boat operation out of somewhere along 7 mile beach...
the most fun we both had was on a self planned shore snorkel only dive somewhere just South of the cruise ship port. I have only sketchy memory of where we parked and got in. Looking on google map I think it was somewhere around the Eden Rock Dive Center on S Church Street. We spent hours on that reef, there were huge tarpon and tons of life. Lots of relief on the reef as I recall with large slot 'canyons' to explore. Diving the North wall on SCUBA was an unforgettable blue color, but I think we both agree the most fun was on that snorkel dive (& I have always preferred deeper and more challenging dives so that's saying something)