Is the OBJ value of a plane, the max points you can earn by damaging it? (including an additional 1.0 point for "killing" it.)
Ok, you are more cinfused than I thought
The OBJ rating of your plane is the one that is used to determine perks gained by killing structures - town buildings for example. It's only used for that single purpose. And for that purpose it works the same way like ENY rating works for determining perks gained by killing other planes.
Kill another plane or vehicle: perks gained = (Your ENY) / (Enemy ENY) x current perk bonus modifier x landing modifier
Kill a building: perks gained = (Your OBJ) / (This structures OBJ) x current perk bonus modifier x landing modifier
Note that unlike score points, damaging stuff doesn't give perks at all. Only killed planes or objects result in a perk gain.