We are not: it depends on the conflict.

When one military force blends in with the civilian populace, actual civilian casualties will fall somewhere inbetween extremes (100% of those killed and 0%).

Ergo, excessive casualty ratios indicate that either (a) the enemy military force is larger, (b) the IDF is exceedingly good at killing only enemy combatants without taking casualties, or (c) a large number of civilians are being killed.

I don't think anyone would argue that Hamas has as many fighters as the IDF?

I don't think anyone would argue against the fact that the Geneva Conventions require combatants to distinguish themselves from the civilian population.

When Hamas fighters repeatedly, strategically, and intentionally fail to do so, I think they bear significant (and even the majority) responsibility for the resulting increase in what you call "actual civilian casualties".

The onus should still be on the more technologically advanced military to justify their operations.

Just because the enemy is harder to find doesn't give blanket license to level apartment blocks because it's easier.