Sets the factor by which
cameraDistanceMax 15 is multiplied.
If the product of this value exceeds 39, the max distance will be 39. The camera can not be zoomed out beyond 39 yards.
- 1 - 2.6
- When set to 1.9 or higher it will reset/clamp back to that value on relog or /reload  
Changing the slider maxValue before PLAYER_ENTERING_WORLD will remedy this (the clamping will be fixed in patch 7.1) 
CameraPanelOptions.cameraDistanceMaxFactor.maxValue = 2.6
Changing this setting
In-game, type the following
/console cameraDistanceMaxFactor setting
Alternatively, you can exit wow, open the Config-cache.wtf file, and add the following line:
SET cameraDistanceMaxFactor setting
You can also use the SetCVar Lua function to modify it:
/run SetCVar("cameraDistanceMaxFactor", value)