Minion tracking question

I just started playing as a summoner and I have some questions about tracking my minions.
First, is it a bug or a feature that in the top left corner (where auras and buffs are shown) not all minions are displayed? It seems like there are never more than three icons, and sometimes not even three show up, even though the minions are alive.
Is there any way to make it so that all active minions are always displayed there?
I checked all the settings that could affect aura visibility.

And what exactly is considered a “corpse”? They clearly don’t appear from every monster - is there some kind of chance involved?