When do you top off?

I had a 2002 Xterra that the cats disintegrated on, and caused massive oil consumption as it scored the cylinder walls. It would drink a quart every tank of gas. Near the end I just started adding oil when I heard the lifters clattering or saw the idiot light come on at idle. Actually I would add the used oil from my other cars lol.
 
Since all my cars have a capacity of 4 qts or less I'm hesitant to let them go all the way down to the fill mark. 1qt low on an engine with 4 qt capacity means it's running only 75% of it's full capacity. I try to catch it when it's approximately 1/2 qt. low meaning the engine still has 87.5% of it's full capacity. My Nissan Versa doesn't lower the oil by 1/2 qt between changes but it only takes 3qt. 6 oz. so a full qt. low would be over 31% of it's full capacity. Even 1/2 qt would be over 15.5% of full capacity.
 
I try to check the level about every 1K miles. If it is down to 3/4 of the space between the two marks then I add. The biggest PITA is that my 2016 CR-V really requires you to wait 10 minutes after you turn off the engine, and then again 10 minutes after you add. And if it takes multiple adds to get the level correct that is 10 minutes after each add.
 
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