I partially disagree with this. With the reputable vendors such as Winexpert and RJ Spagnols, I've had lesser results in recent years with shorting the water. The kits are balanced for a 23 liter reconstitution, and adding less throws off the acid, making them sharp. This is true for their lower end kits.On the cheaper kits decreasing the water improves the structure and depending on the kit the abv, will adjust itself accordingly
Other kits? I'd still reconstitute to the full 23 liters, trusting the vendor has balanced the kit. If the vendor hasn't? I'm of the "wait-n-see" school of thought, so I read a lot of reviews before buying anything.
IME it makes more sense to add to the kits to increase body, e.g. raisins, currents, more grape concentrate, etc. One thing I haven't seen included in kits in at least a decade is dried elderberries. I recall red kits often included a packet of dried elderberries to increase body.