There is a rather comprehensive thread on this subject here:
Dwarf Thunderer Champions
I know a lot of people get all hot and bothered about the prospect of making their S&S at a faux short thanks to the presence of a poor-range weapon. This kind of "Wait for it!" charge reaction was a part of 7th edition (the charging unit was effectively halted at the range where all models able and allowed to shoot were in range), so I can see why people would want to bring it into 8th as well.
For your convenience, a rules quote:
A Stand and Shoot reaction can be declared against an enemy unit that starts its charge outside the firing unit's maximum range - the shooting is resolved normally assuming the enemy is just within maximum range of the shooting unit's shortest-ranged weapon. If the charge fails, for whatever reason, we assume that the chargers closed to within the weapons' maximum range before being driven off.
Now, in any S&S the chargers will either a) start outside the maximum range of the unit or b) within range of one or more models.
In the case of a) there are rules about how out-of-range weapons get to shoot at their maximum range, and this part is kind of open to interpretation towards the "Wait for it!" mechanic. I say "kind of" because a lot of people do, and I don't think they are idiots; they obviously see something here. I guess it's something like this:
"...the [unit's] shooting is resolved normally [by] assuming [that] the enemy is just within maximum range of the shooting unit's shortest-ranged weapon [for each shooting model]."
In case of b) the rules say... nothing. Apparently no exception to normal shooting applies if some models are out of range, and for normal shooting that means they don't get to shoot.
Personally, I think they should have kept S&S shooting on a model-by-model basis rather than involving the unit level. I don't see the problem with some models shooting at long range and others at short range (you know, just like normal shooting) with the added clause that any models with out-of-range weapons get also to shoot at their weapon's maximum range - because the target is essentially moving from out-of-range into close combat!
-T10