Does Range Weapon Profiency increase the range for both hip-fire AND while aiming down sights (ADS)? Or does it do that just for one of those?
Weapons have two sets of damage tables - one for "close" range and one for "long" range. Past long range, the gun does no damage at all. (This is mostly of interest to close range weapons such as shotguns and SMGs)
The "Range" proficiency extends both the location of the "close" to "long" range drop off, and extends the "long" to "none" range dropoff.
ADS and hip fire effect the accuracy of your shots (ie, how many of the bullets you fire end up where you intended) which may have impact on the effective range of a weapon to an extent, but this is not effected by the "Range" proficiency.
For instance, if you fire a shotgun shell without ADS, 3 of the pellets may hit, causing 3*damage_at_current_range. If you ADS first, 5 may hit, causing 5*damage_at_current_rage. The value of damage_at_current_range depends on how far the two players are apart, and is modified by the Range proficiency.
Your accuracy without ADS is modified by the Steady Aim perk, which gives you a better chance of hitting with more rounds when you hip-fire, but not as good a chance as with ADS.