When there are a lot of uses at less than 1 GPM like a swamp cooler, yes a little larger tank is recommended. Since you have the kit with the 4.5 gallon tank, the pressure switch is close to the pressure tank as it should be. So now you can add an additional tank anywhere after the kit that you can find the space. You can tee in an additional tank right after the PK1A kit or somewhere else in the house like under a sink or next to the water heater. I have two swamp cooler here at my shop, and I use a 20 gallon size tank. Although, because of how the CSV works, you would be surprised at how few cycles you get with just the 4.5 gallon size tank.
