Neck Relief Factors
The 4th and 5th strings vibrtating arc is even larger than the 1st string
A plucked string has a vibrating arc which is greatest at its center. Neck Relief is the intentional curve in a neck to compensate for the larger size of that strings' vibrating arc at its center. This intentional curvature is intentional to prevent buzzing on the frets. Neck relief is accurately measured in thousandths of an inch or sometimes by 1/8, 1/16, 3/32 etc. Some relief is necessary or the strings will buzz. Heavy strings require more relief and lighter strings less. Also string scale length has an effect. A long scale classical guitar has a standard 26” string scale and a larger vibrating arc than a Fender Strat which has a 25.5” string scale (string scale refers to the distance from the nut to the bridge on the 1st. string.) A short scale length would be something like a Gibson or Martin guitar that has a 24.5“ string scale. (I believe Martin uses several string scales, Gibson may also). The trade off is that a short string scale has a smaller vibrating arc and may achieve better playing action by getting closer the frets but looses volume because the smaller vibrating arc makes a weaker signal to the pickups magnets. Being so close to the magnetic pickups actually dampens the string, pulling toward the magnets and reducing sustain. There are many trade offs and unexpected relations between magnetic pickups and steel strings.
Ultimately, neck relief is a balancing act between several factors. Some trade off is necessary. If you go from light guage strings to heavy there will be some string buzz and adjustment will be necessary. Relief May increase due to the heavier pull of heavier strings. This depends on the inherent stiffness of the neck. Some necks are stiff and others are not. Each instrument has its own character. If your instruments neck is in a delicate state of balance going from hot to cold can often throw your neck out of adjustment. Moisture and humidity also affect neck adjustment.
These are the three basic characters a neck will display. Your neck will fall into one of these catagories