[untamed]

OK...assuming that is a pretty large pipe joining the two tanks....in your new drawings the fuge and sump are connected and will act as one single tank. The water level in each will always remain equal height. It doesn't matter where you put the return pump, the behaviour will be the same.

That will also enable the water to flow silently between them. (assuming both ends of the connection stay under waterline) I imagine that the end effect will be a very deep sump in order to keep adequate depth in the fuge.

Imagine reducing the size of pipe that runs between the two tanks. At some point, the pipe gets so small that the fuge needs to generate more head pressure to push through the water that is coming in. At that point, the fuge water level starts to rise in relation to the sump and you've created an non-adjustable Herbie.

If the pipe is too small to carry the incoming flow, even when the fuge is full (max head pressure), then the fuge overflows.

The bottom line is...if you put a gate valve on that line, you'll be able to adjust the water heights between the fuge and sump to whatever you want. If you want 10" in the sump, and 11" in the fuge...you can do it. Sump level is controlled by the total amount of water in the system...fuge level is controlled by the Herbie valve. Just make sure you have an emergency overflow on the fuge.

My answers are very long-winded. Why don't you just call me, or come visit? PM me if you are interested.