Lots going on here.
1. Left and right differences are normal. Most cars do not weigh exactly the same for each side.
2. Your coilovers do have preload adjustment. The adjustable perch that the spring sits on adjusts preload. Preload also affects ride height.
3. You should pay attention to both preload and shock length when adjusting ride height. Preload for 1 set up may not work for every set up.
4. Many people and even many manufacturers simply do not understand spring preload. It's one of the most common coilover questions and it frequently gets many of the same wrong answers.
Read this:
https://www.instagram.com/p/B9J1M8Un..._web_copy_link
^That won't give you all the answers, but it will give an overview.
I would recommend at least following Tein's recommendations for preload.