Accuracy of aeromotive sending unit

Ok finally got some time to mess with the tanks inc sending unit. With a half a tank of fuel left my gauge would show empty. I dropped the tank out of the car today and ran some electrical jumpers from the sending unit to the cars sending unit connection along with a dedicated ground for the sending unit. I started with measuring the tank depth divided that by 2 and used this to home in on roughly half a tank. I measured from the sending unit mount gasket and used 4". This got me close at a half a tank. My biggest concern is the big "E". I had to mess with the sender by moving the rheostat up and down on the bracket as well as adjusting the length of the float arm. It is much better now. I set it up to when it indicates empty I have a reserve of about an 1/8th tank. The only issue is it will hang at full longer. I tied into the car this way because I figured due to variances in wiring etc I could fudge that out some. I have just at a 1/4 tank and my gauge now indicates a smidge under a 1/4. I also adjusted the tabs at the bottom of the rheostat housing to prevent the arm from over traveling. As far as the instructions from Tanks inc on the sender their dimensions didn't even get me close. This isn't a fault on their part I don't think, I just believe its inherent to the electrical in these old cars. I am also using a digital 5v voltage regulator on the cluster. So as I stated each car will have some variances in the system I believe. The meter match may be an easier approach but I kind of like to tinker with what I've got to see what I can make work. Hope this helps out some.