I don't know about Jeep tires in specific but in general the pressure on a tire's sidewall is the maximum permissable pressure.
In general the maximum weight capacity of a tire varies with load, inflation pressure and speed (and required tire life) to keep carcass temperature within acceptable/survivable limits so
ifthe tires have more weight capacity at maximum inflation pressure than needed for the vehicle, inflation pressure can be safely reduced (to a pressure determined by the manufacturer) to a lesser value. According to Coker's web site max weight capacity of their Firestone 700-16 NDCC tires is 1800 pounds at the 45psi inflation. According to the M38A1 CDN2 Operator's Manual, I see maximum permissable gross weight of the winch equipped version as 4080 pounds on highway (less for off-road or without winch).
From the web, here's a link to a set of Firestone load inflation charts https://commercial.firestone.com/con...s_web_2014.pdf Unfortunately, they don't list bias ply 700-16 tires in the charts but the chart should give an idea of the relationship.
Assuming even weight distribution at the four corners of the Jeep, I see the charts as suggesting that the 28psi value may be OK. In the end, it is your Jeep, your tires, your life and your judgement/decision that matter.