Those plots look to me like what you want a plot to look like, a long shape, that means your heart beats are nice and variable. That makes sense if you were tracking all night. The time you measure affects HRV because your position and activity and metabolism will alter the beats, so you want to compare same tracking time to same tracking time. Like 2 minutes to 2 minutes or 5 minutes to 5 minutes, or 24 hours to 24 hours.
The shorter that oval in the poincare plot is the less range between the longest and shortest beat intervals. Plots like this can be used to determine if you have unusual beats or the equipment isn't working. Then you'll get more outliers. I don't know what that flying saucer shape on the right means, but I don't think you have too many outliers to suggest skipped beats.
I took a PhD level class on HRV biofeedback (HRVB), which is when you use lab equipment or cheaper software like stress eraser or heartmath or even a breath pacer to make your HRV go up. It goes up anytime you breath at around 6 breaths per minute (10 seconds per breath) because of a resonance frequency with blood pressure. That is why heart math is pre-programmed to use that breathing speed although you can change it. Adult people have similar enough blood volume that somewhere between 4-7 breaths per minute is always going to create coherence. It really has very little to do with the emotional part and breathing through the heart, its a straight up biohack.
For everyone the heart speeds up when you breathe in and slows down when you breathe out, but when you breathe at a certain pace which syncs with the momentum of the blood in your veins and the time delay (5 seconds) in the stretch receptor mechanismsin the cartoid artery, it creates greater HRV thus higher values for stats like RMSSD and PNN50, SDNN etc.
Academics consider the simplistic interpretation of parasympathetic and sympathetic control relating to LF and HF HRV outdated. There evidence that the parasympathetic nervous system can affect both values.
Also that interpetation only holds for a certain rate of breathing. The rate of breathing will vastly affect your HF/LF ratio and if it is slower than the normal person (normal is around 15 breaths per minute, slow would be like 8 or 10). it will make you look way sympathetic dominant according to those simplistic interpretations. Unfortunately it is hard to track your breaths because you automatically breathe slower when you count. There may be a motion sensor app you can put on your chest when you are reading or something so you forget or you can have a friend or girlfriend spy on you.
So Altini recommends taking your HRV each morning at the same rate of breathing. Though this ignores the possibility that slower or faster breathing is related to health. There is some evidence that those with PTSD slowed their resting breathing rate, improved their resting HRV, and improved their symptoms all at once as a result of HRV biofeedback.
Anyway hundreds of studies for HRVB show improvements in resting HRV stats AND most importantly improvement in whatever clinical condition was being measured (anxiety, depression, pain, heart disease, asthma, etc), after practicing resonant breathing for awhile, say 4-6 weeks, 10-20 minutes 1-2x a day 5-7 times a week. It isn't known though how long these changes might last if you stop the practice. It isn't known by what pathway it helps, possibly something with toning and exercising the vagus nerve. Sometimes, even often, the clinical improvements happen without improvement in resting HRV over time.
All this said I do not have a paper with the average healthy or optimal values you are looking for. I asked the same question and my professor told me rather rudely that it was in our literature, but didn't tell me where. So all I have are research papers with the resting values of various populations studied from shortish measurements 2-10 minutes. I can upload articles here if you are interested in anything in particular.