That's true, variations exist withing the general formula. However, 80/20 is a good starting point since the hardware is pretty much a constant. In other words, if the hardware allows a 80/20 lamp to function properly (standard stuff, same light bulb, same wattage, same construction, same bottle, etc.) then it will also perform (with slight variations), such as 85/15 or maybe even 90/10. There will be adjustments required for the liquid however, to compensate for the reduced amount of wax and increased amount of water.
For instance, a 90/10 lamp is likely to run somewhat cooler than a 80/20 lamp. More water, water is a great heat exchanger, hence the lamp is likely to run a few degrees cooler, at operating temperature. A cooler lamp will affect the behavior of the wax within the lamp and it is this change in behavior that will need to be compensated for with adjustments in salinity and/or tweaks to the surfactant.
Gliter based lamps are likely to behave uniformly within the parameters of 80-90/20-10 range, with perhaps a slower flow in a cooler lamp than in a warmer one.
the ratio isnt constant. the early crestworth and also lava lite bottles had less wax , there is a comparison pic somewhere on this forum.