Propane exchanges

I found it difficult around home to find a place that refills propane tanks. Here in Texas apparently there are more regulations than other parts of the country (for example Oregon, where you can get it filled at many corner gas stations). There are a number of propane dealers near my home, but they don't fill, just deliver to homes, businesses, etc. I had to drive a little out of my way to find a place that does fill. The owner was very nice, and he explained after inspecting my tank that exchange refill tanks are about 15 lbs empty. My tank that came with my 172 was just over 16lbs empty (I know it was empty because I accidently left it open while connected to my backyard grill and burned it all). I'm assuming that a heavier tank is a better quality tank, so I'd prefer not to exchange it as the inspection is good until 2020. He also informed me that the refills don't fill the tank all the way, they put 15 lbs of propane in, where he put 20lbs. The cost was $18, where an exchange would give me a lower quality tank and 25% less fuel for around $20. I know that some space in the top of the tank is required, because the liquid propane needs to evaporate into a gas to exit the tank and be consumed, but I think there'd still be plenty of room with 20 lbs.  Seems like a no-brainer to me.

All modern portable LP tanks have special valves which keep fill stations from totally filling the tanks. If the tank were completely filled and not used right away...some of the liquified LP would bleed off to keep the tank from being over pressurized.  In the past, a lot of LP was vented because of over filling.
I prefer to have my own tanks refilled...I then know that the tank has been filled to the max 85%. Here in MN, the largest tank exchange company was caught not filling the tanks to the 85%.  They pocketed the extra profit even tho' they were saying that the tanks were filled.