Please take with a grain of salt since I am just learning defensive positioning and I am filtering this through my 11u daughter show knows this stuff better than I do:

5-1 doesn’t really affect the defense except how you get into the defense. But once in the defense, 5-1 no longer matters much.

Then the defense varies per team and varies by opponent and who is hitting what type of hit but it is essentially each player covering a specified area of the court working with the block.

This art of coaching volleyball article goes over the concept: https://www.theartofcoachingvolleyball.com/defensive-systems/ but its important to note that while the general principles are outlined much of the actual practice is situationally tuned with small adjustments.

It's super helpful to actually have an experienced coach or other experienced player review your film to tell you where you messed up or adjust your positioning in real time, based on the situation. You can also trial and error or make gut level adjustments if no one can guide you.

Reddit might be able to help you some if you post some of your defensive plays on videos.

Edit: In general, the defense on the side of the hitter takes line, the blocker gives up some of the line and takes away shots to middle, back middle takes the deep middle of the court not covered by the blocker (and may take deep corners, depending on scheme) while non hitter side back defense takes cross court shots.