Yes, all the charter companies have this restriction. The issue is that if you make a navigation
error outside of the reef (like when attempting to enter a cut from offshore) then the result is likely to be catastrophic. And of course you are much further away from them for support.
Re N of Belize City. The cruising grounds are better in central to southern Belize -- starting from south of Belize City. N of Belize City the water gets shallow and your options fewer (although I do like Caye Caulker and St. Georges Caye).
Tobacco Caye is one of my favorite places. Funky little Garifuna village on a very small island. Couple of bars ashore and the lodges ashore can sometimes accommodate you for dinner with advanced notice (if they have guests already). Assuming you are chartering a cat (shoal draft) then you can anchor
a bit north of the caye on the sand flats (gets a bit shallow close to the caye) in about 6 ft of water right behind the reef...waves crashing on the reef just in front of you and water like a swimming pool where you are anchored. Great snorkeling just to the south of the caye along the edge of Tobacco Cut. Only 14nm from Tobacco Cut to Glovers Atoll. Most days someone will be running in a skiff between Tobacco and Dangriga so you may can get them to pick stuff up for you in Dangriga if needed.
Southwater Caye is a bit like Tobacco's slightly larger and more sophisticated older brother. Nicer lodges there, who may also accommodate you for dinner with advanced notice. Blue Marlin Lodge has a bar too. Also, they are friendly and helpful...you can sometimes buy ice, water, and small amounts of fuel
if they can spare it. Good snorkeling just south of Southwater too and across the cut at Carie Bow Caye as well.
Great short sail between Tobacco and S'Water, just inside the reef, going either direction in prevailing winds.
Usually when running out of Placencia on a week long charter, I don't go any further north than Tobacco. Remember, you are going against prevailing winds and current
to get there from Placencia (do this in the early AM... the inner channel can get a bit rough after the afternoon sea breeze picks up...or hop your way up over a couple of days...plenty of stops along the way: Lark Cay Range, Wippari Caye, Pelican Cayes, Lagoon
Caye...). Then you can turn around and go with prevailing winds and current
to return to Placencia...pic attached...barreling back into the N cut into Placencia Harbor after a charter (a route
discouraged by Moorings...common spot for boats to go aground).