Depends on whether or not you're adding nutrients...most nutrients will have an acidifying effect...make the pH go down.
You want to measure the pH of the solution after everything is mixed in...the "final pH" of the solution...
But yes, you generally are looking to feed/water with the pH you desire...except in cases where you are trying to CORRECT
pH issues (such as your 7.8 pH) at which point you can adjust to UNDER the desired range to have more effect, like feeding/watering
it with 5.7 pH or 5.8 pH to bring it down into the range you're looking for.
In general, you want a "sweep through the range" of 6.2 to 6.7 between wet and dry...dry will be your high point in the sweep and wet should
be your lowest pH in the range. That way you guarantee that there will be a pH present in the soil at some point during that wet/dry
cycle that is wheelhouse for each particular nutrient's best uptake.