While many people cite the changes in body and fermentability that can come with changes in water to grist ratios, the impact from 1qt/lb (~ 2l/kg) changing to 1.5 qt/lb (3l/kg) is not noticeable at all, IMO. I have only noticed the impact when going from 1qt/lb to 3 or more qt/lb.
The main concern with calculations is that if you are batch sparging you can expect a larger run off volume with more water in the mash (obviously). That only comes into play as you are calculating (estimating) your sparge water for the second runnings. (I supposed this also plays into ohm much sparge water is need for a fly sparge set up too).
If you are just getting started with partial mashes, don't fret over this too much yet, its a small small trivial factor in the final beer. Stay focused on hitting proper mash temp constantly and getting good sparges. Stick with one water to grist ratio too, like 1.5qt/lb, for your next several batches. Its about consistency at this point in the learning curve. The fewer variables you mess with the better.