Sorry, I should've been more clear. It sounds like your battery backup is working fine, the goal for the battery backup is to keep water turning slowly as to prolong the life of the battery.
The 20% you referred to is what happens when the pump goes into feed mode, that setting has nothing to do with power outage. You have battery backup set to the lowest setting, meaning you'll get maximum life out of your battery.
I don't know your system and calculated head pressure, but I assume that "lowest speed" will only keep the pipes primed.
What you can do is simulate a power outage by unplugging the power brick and pulling your return above the water and gauge the flow, then toggle through the settings until you get the flow you desire, keeping in mind that you're going to shorten the battery life by turning it up.
And to answer your question about turning off "power on delay". That setting us to prevent your pump from returning to normal if you're the supply power is fluctuating on and off, this will prevent damage to the pump by waiting a predetermined time before transferring power back to normal.