If you set zebra 1 to 60 and then set zebra 2 to 90, then go back to zebra 1 you will find that the displayed value of zebra 1 will now be 90, however provided you don’t make any changes to zebra 1 if you go down to BOTH zebra 1 will work at 60 and zebra 2 at 90.
The thing is that going back to Zebra 1 (or zebra 2) and make any changes you select selects Zebra 1 (or 2) only, ie a single zebra and in doing so sets the level to the last level set. It’s only by going to BOTH that you enable both zebras together.
So to set two indendent zebras first set zebra 1 to your required level, then set zebra 2 to your required level, final scroll down to both and select. Now you zebras will be working at the independent levels you set, even though this may not appear to be the case in the menu.
It’s not the most logical way to lay out the menu as it does not show you both settings together at any point, hence the understandable confusion, but you will find that both zebras will work at the independent levels you set.