Hi bro divinesloth, I do face casualty also. However, I like to have my rock scape made with many holes or craves for them to swim and hide. Having said this, selection of fish is important but I personally felt a feeding one may not be a stable one but higher chance. Yrs is brazil or african flameback? I understand brazil is more aggressive. I adopt the masslogy to prevent dominant fish. Like the louhan concept and prevent them from establishing themselves. However, for wrasse, if u want to keep, suggest u keep their genre , tame vs aggressive. Mixing them may cause casualty. Now going into angel which seems harder. Few methods:
1. Mirror
2. Rescape
3. Existing scaling with many hideouts
4. Get a bigger specimen
5. Hantan few new fishes at one go but many will not encourage this. However, it works for me.
6. QT
7. Customized made betta box and placement in the tank
8. Quarantine the aggressive fish if possible
9. Order of fishes to put in
10. Having said the above, luck does play a part.
Hope this helps.