From a band 3 school ...
. No need to thank me in future ...
Looking at how much RAM left or unused is relatively meaningless ...
RAM is for apps to run, then subsequently they become "garbage". Bigger RAM can hold more garbage henceforth more apps/processes can be opened and stored. They will be quicker to recall when needed, rather than open again.
Then said, Android has its memory management policies such that it would limit the number of processes kept running in RAM.
So upon reaching a certain RAM capacity, "extra space" would not help much ... The "garbage collection" process has been preset.
If you are really obsessed of unused RAM, you can reduce the number of processes allowed; the setting is at the Developer Option. You'll then see lesser RAM used hence more free RAM will be seen.
In this way, more reading, writing, overwriting etc will happen when launching apps. That will reduce the performance of the OS and increase battery consumption.
Therefore as a whole, RAM is supposed to be used up as much as possible. More apps or processes to be kept at the background such that overall performance will be improved.
However, battery consumption will also be increased.
Hence it's a balancing act between performance and power consumption ...