SOS satellite coverage

I've tried to use the satellite SOS feature on iPhone 14 Pro Max at about 20 miles offshore in Florida on the gulf and it reports "not available in this region". However it worked at about 5 miles offshore. Tried this on several trips and consistently fails beyond near shore range.

Is there a coverage map available? I bought it believing it would be a good backup emergency safety device when offshore but that's not panning out.