Your heater core is under the dash, but if it is leaking your floor might not be wet. My 94 Ranger (I imagine your 93 is the same) has a plastic tray under the heater core, with a plastic tube thru the firewall. When my heater core leaked the antifreeze ran thru the tube and out onto the ground at the right rear of the engine.
Get a good light and watch your motor while it's running. Look for the highest point at which you can see antifreeze. Wiggle your heater hoses around -- I once had one where you couldn't see the leak until you wiggled it. Sometimes while you are driving, the antifreeze can be blown around so that it makes it hard to tell where the leak really is.