All I know is taking the "proper dose" of Prednisone is very complicated!

Prednisone replaces the hormone cortisol which your adrenals produce. Your cortisol levels are variable during the day depending on many factors such as stress levels both physical and psychological, infections, and whether you are active or sedate. The amount of cortisol in your system is regulated. Cortisol levels are high when you need it and low when you don't need it. The body has a mechanism to regulate cortisol levels and it is called the HPA axis.
https://www.verywellhealth.com/hypothalamic-pituitary-adrenal-hpa-axis-5222557#:~:text=The%20hypothalamic%2Dpituitary%2Dadrenal%20(HPA)%20axis%20involves%20the,adrenal%20glands%20to%20release%20cortisol.
Prednisone overrides the HPA axis and takes this mechanism out of auto pilot. There is no such thing as a normal dose of prednisone because your body's need for cortisol is variable and depends on all the factors already mentioned.

The best you can do is to take enough prednisone to meet your body's needs. Your 5 mg dose of prednisone is called the physiological dose. It is enough for your "average days." It might not be enough for those days that aren't so average. That is why you have good days and not so good days. It is hard to predict what a day will be like so therefore it is hard to know how much Prednisone to take on any given day.

Approximate Prednisone Dose Ranges
Physiologic: 5mg (usual average adrenal output)
Supra-physiologic: 10-20mg
High supra-physiologic: 50-250mg (max adrenal output)

In the following link there is a table about Prednisone doses depending on the condition being treated. The overall Standard dosage for adults is anywhere between 5–60 mg per day depending on the condition and other factors.
https://www.singlecare.com/prescription/prednisone/dosage
The normal range for PMR is said to be somewhere between 5 -25 mg. Your 5 mg dose is in the lower range but generally you should take the lowest dose that is effective. It is better to let your doctor help you decide what prednisone dose to take. The patient is in charge of monitoring their symptoms and communicating to the doctor what those symptoms are. Anything else is called "self medicating" and that is frowned upon. However, self medicating happens all the time.

I wish you well and I hope things go well for you as you progress in your PMR journey. Everyone has a different journey so there is no "correct dose" of Prednisone. However, a "stable dose" is important because the body likes stability and maintaining homeostasis.

"Homeostasis is defined as a self-regulating process by which a living organism can maintain internal stability while adjusting to changing external conditions. Homeostasis is not static and unvarying; it is a dynamic process that can change internal conditions as required to survive external challenges."