DPT as Level Transmitter for Surge Vessel

I assume that your distances are true elevation differences (with reference to a plumb line) and not horizontal or angular distance values.

Therefore, how can "values of height & they don't correspond to corresponding pressures" be true?

2.27m H2O = LRV = 4.0mA = bottom of the tank
8.57m H2O = URV = 20.0mA = top of the tank

In your initial query, you provide the conditions for a level measurement with water as the medium, "a surge Vessel for a water application".

Water has a specific gravity or density of 1.000, which is taken into account for the engineering units of mm H2O or inches H2O.

A column of water is a column of water; it exerts a force on a diaphragm of known area and the result is pressure.

Therefore, the height of the water column is the level or the elevation distance.

Pressure transmitters measure pressure in various units, several of which are head pressure in water units, for instance, mm H2O, or for us Americans, inches H2O.

The LRV and URV are elevation distance values, corrected, if necessary, for specific gravity, but in your case, no correction is necessary because engineering units in water column are used directly for water applications.

The level LRV and URV both take into account the mounting of the DP transmitter below the bottom of the tank.

Tank volume values are calculations using the level value which is then multiplied by some scaling factor. But tank volume is not a level transmitter's LRV or URV, level is a transmitter's LRV and URV. Usually tank volume calculations are done outside the transmitter in the indicator/HMI/PLC/SCADA/DCS/whatever.