Balancing Dispensing Pressure

My father has a tap attached directly to the disconnect on the top of his keg and I am trying to balance the dispensing pressure. Unfortunately when you try to use the typical balancing equations there are too many zeroes that make the formula not work. Does anyone know what psi range is about right for dispensing with no line length? Also, since the pressure will have to be very low, when the CO2 starts to equalize as the beer level goes down is there a psi increase that needs to take place?

Very low, I have one of these configurations, I use very rarely and only for picnics/ parties etc…when the full keg will be rapidly dispensed if not lugging the coldplate around. Typically the beer in the keg will be at/ around 2.6 volumes and I need to use only 2-3 PSi or lower to draft.

Exactly. So with this setup for main usage you will have to simply keep the balance correct at all times, So ex. 38 Fahrenheit keg/beer X 12 PSI will equate to 2.5 volumes. Then when drafting you will have to shut off the main gas supply and use the PRV to reduce most all backpressure on the keg then draft a couple over a few hours and then turn the gas supply back on (e.g 12PSI etc…) until the next “session”. This type of scenario is the only thing that will work to keep the keg at the right volumes at all times or else, yes it will eventually “go flat”.