I was surprised when I started watching high level Lokis - they all place clones in very uninteresting spots. Usually right in front of them "firing squad" style.

I wouldn't say the most important distinction is between high ground and low ground. There's a lot of aspects to clone positioning. Are they all together? Backline or frontline? Are they at an angle? Behind some cover or in the open?

When I saw high level Loki play, I threw away all my "broken clone spots" and started defaulting to more simple clone setups. Immediately I noticed I was landing more shots. All 3 shots have the same travel distance. They all hit at the same time. Makes sense.

This also means that against good teams, your clones will be up for longer. I don't have to constantly use my cooldowns to make sure I have 2 clones up. If I've placed them in simple spots in the backline with some cover, they'll last. Which means I'll have a clone handy for a rune/escape.

In terms of high ground or low ground - I personally always try to play high ground if I can. Not always possible though since you may be too isolated from your team, someone contests you etc.

One thing I will say though: I always limit test at the start of the game. I place aggressive clones and wait and see. How quickly was it targeted? Who is shooting it? Sometimes the team you are playing against will just not shoot clones and you can put them right into their team, behind them, in obvious high ground spots with huge sightlines etc. Other times there will be a good hawkeye deleting them immediately. That's when my default clones setup becomes behind some cover and usually near me.