In this tip gear ratio is not main focus. Main focus is feeling and seeing the rod tip while trolling at 1.8 mph. Then when you cast and retrieving you try to mimic that same rod tip bend and that same feel of pressure, so you can estimate a 1.8 mph retrieve while reeling. 5.1 will be more cranks than 6.4 but don’t worry about that. Focus on the feel on rod tip / pressure and don’t focus on the reel.