Just so we are clear...
If you do a preinfusion pull, that water volume gets eaten up in the puck (pretty much) and so that pull doesn't count as part of the shot volume creation. The next pull creates approx .5floz and if you didn't pull again that's pretty much all you would have in the cup... ok there would be some minor fluid addition from the preinfusion pull, so maybe .6floz.
Another pull will bring your in-cup total to approx 1floz or a touch more (or less) depending on how much the coffee puck in the PF holds on to as a saturated mass.
Personally I don't think a 15gm dose resulting in a .5floz cup is the way to go with the PVL.
Maybe try capturing the first .5floz in a shot glass and then switching to another shot glass for the other .5floz. Taste them side by side and of course they will be different. The key is... the two cups require each other to create a balanced cup. And by balanced I don't mean in the SCAA sense, I mean in the 'what the espresso can offer' sense.
What is it that you don't like?