At some point (especially in the hanger right before they escaped), sure. But I seriously doubt it [troops missing on purpose as to track them to the rebel base] was happening from the second they landed on the Death Star. That strains credibility by quite a bit.
No, not right away. But as soon as they bust the Princess out, I’d say the plan was made and orders given. The only scuffle before that is when Luke n’ Han are dressed as troops and take em by surprise.
Surprise that somehow lasted 10 minutes while a bunch of em apparently ran around the room doing nothing but looking for their guns or something, but ok.
This also ignores ESB where they can’t hit anything because of “tight corners” as you put it, never mind that the heroes had no problem with that.
The answer, as in most movies, is that the faceless enemy can be shot while the heroes can’t otherwise the movie would just come to a screeching halt. It’s nothing more than the mechanics of making a movie like this.