I think the biggest difference to the way I use my system, to the way that other use theirs, is that I have no dump load - in fact the main load (the filter pump on the swimming pool)
IS the dump load!!
I charge the bank until the charge counter says its full or I hit my maximum voltage (max safe value for the inverter) and then run the load to use 10% of the accumulated charge (or 1% if I'm just trying to pull the volts down a bit!).
I'm only using 10% of charge as I'm planning on my batteries lasting at least 10 years :-) The other 90% is then always there for emergencies as well!
The final graph on the display shows the total values for amp-hrs in and out. I guess the average charging voltage is about 26v and the discharge value about 24 so although the current loss is only 13%, the power loss is probably much nearer the 20% you expect.
Cheers