The idea is for the pressure at the top of the system to never go negative, which can potentially draw air into the system. If the highest point of the heating system plumbing is only 25' higher than the pressure gauge, it's normal to pressurize it to (25' x 0.43 psi/ft) + 3 psi= 13.75 psi, call it 14-15 psi, in your case. The + 3 psi it to give it some margin, to cover pressure deltas that crop up when the pumps are running.
But measure it- in most homes the pressure gauge on the boiler is well off the basement slab, with maybe 6-8' between it and the first-floor radiators, and maybe another 10-12' to the baseboards on the second floor, for maybe 20', not 25. That comes in at 11.6 psi , call it 12. With high-ceiling construction and tall radiators you might need to bump it to 15 psi, but most 2- story houses are just fine at 12.
You pre-charge the tank to the system pressure, not conversely. Many tanks come pre-charged to 12psi, but that has to be checked prior to pressurizing the system, and adjusted as-needed. If the tank is more than a few feet above/below the pressure gauge, you may want to run the math on it's pre-charge level to cover that pressure difference. An expansion tank located 10' above the pressure gauge should be set 4 psi below the system pressure measured at the gauge. If it's within a couple of feet (as would be typical), fuggedaboutit, it's not enough to really matter.