Making more coast graphic variations will be too difficult, technically, that it's not worth it.from the graphic it would appear to be intended as shallower safer water closer to land and that's what i have always thought of it as. and its greater yields were because it was easier to reach with less loss. it also works blocking access to different areas early on if removed around parts of the coast. resources on the water represent richer fishing areas. if coast is meant to be non depth representative then the graphic should be changed to represent it. you could instead make a dangerous coast and a safe coast where ships take damage passing like the difference between northern Scottish and Irish coasts and Caribbean beaches. have them be exclusively touching land and early ships should be restricted to them. you could then get rid of the reef tile and have a similar lighthouse building to negate the effect of dangerous coasts, give them less resources until a lighthouse is built as well. have the rest be either ocean or continental shelf where you can do different things in future areas and different resources spawn or something.
Reef does the job well, of making dangerous coast I mean.
Even having polar- tropical- normal- Coast creates graphical glitches.; So I would prefer it if all coast terrain use the same textures.
Edit: Continental shelf is indeed shallow water but does not need to be close to land (coast).
Spoiler :
Cyan is continental shelf.
