I play this by ear.
this is just s coating usually , maybe a bit more
Id say for just a coating for an individual portion of pasta
a generous tablespoon would be a good starter. maybe about the same of water.
you want it smooth and a little thicker than heavy cream. you add that to the reduced sauce you made
mix quickly and add hot pasta
the benefit is it acts like heavy cream which is more or less is at this point and won't ' split ' w wine i.e. acid.
you want more creamy sauce ? add more flavorings at the beginning and more cream cheese and water mixture at the end
the reason you add the water to the cream cheese first is so the final sauce is not lumpy but smooth.
try it
report back.