A 20 gallon size tank only holds 5 gallons of water. That is not enough for a 10 GPM pump. For the recommended 2 minutes of run time, you need an 80 gallon size tank, which still only holds about 25 gallons of water.
You have millions of gallons of water stored in the well. Your water comes from the well, not the pressure tank. If your pump quits, you are out of water, no matter how large a pressure tank you have. The pressure tanks only function is to reduce the number of on/off pump cycles. Using a larger pressure tank to reduce the cycling only means your pressure swings take longer.
When using 50 gallons to take a shower, an 80 gallon tank will supply the first 25 gallons as the pressure drops from 60 to 40. About the time you get the water temperature adjusted for the annoying decrease in pressure, the pump kicks on and the pressure starts to climb from 40 to 60. Now you have to start adjusting the temperature again for the increasing water pressure. Before you finish rinsing off, the pressure has climbed back up to 60. So you finally start seeing good pressure, about the time you are finished with the shower. A 20 gallon, 5 gallon draw tank, will cause the pressure to annoyingly swing from 60 to 40 and 40 to 60, many times during the same 50 gallon shower.
A 4.4 gallon tank holds 1 gallon of water. So the pump doesn’t need to start for rinsing a toothbrush or to fill the icemaker. But when you start a shower, the gallon in the tank is quickly used up, and the pump is started. Now the CSV is delivering a constant 50 PSI before you even step in the shower. No matter how long you stay in the shower, the CSV continues to deliver a constant 50 PSI, and keeps the pump from cycling.
A constant 50 PSI makes for a much more enjoyable shower, that when the pressure keeps swinging from 40 to 60 and 60 to 40. A tank that only holds 1 gallon of water may cause the pump to cycle a few extra times a day for flushing toilets and washing machines. However, the CSV makes up for that by eliminating so many cycles during longer uses of water like showers and sprinklers.
Larger pressure tanks don’t solve the problem of cycling. They only cause the annoying fluctuations in pressure to drag out longer and longer. When you use a CSV, the cycling problem goes away. The larger the tank, the longer it takes to drain, and the longer it is before you start enjoying constant pressure in your shower.
I wish I had a nickel for every time I heard someone with a large pressure tank say, “I was half way through my shower and all lathered up, when the water stopped coming out”. Meaning when the tank was empty the pump did not start. Nothing is more inconvenient than having to dip water out of the back of the toilet to rinse the soap out of your hair. This doesn’t happen with a small tank and CSV, because the pump starts before you get in the shower.
Even when they are clean, the restriction from all those filters is much worse at the low end of a pressure switch setting. With a CSV and a small tank your system will go through the low end of the pressure switch and be up to the desired constant pressure before you step into the shower.
You said, “adjusting the pressure up made shower taking a joy”. Imagine the joy of constant pressure. Increasing the size of pressure tank is not the best option.