I brewed last night and used a partial mash. I had a total of nine pounds of grain and three pounds of DME. The estimated gravity was 1.066 based on a 5.5 gal batch. Everything went fine and according to schedule. My boil was about 4 gallons and so I topped off the fermenter with water. I poured one gallon of water in the fermenter with about half of the cooled wort, then pitched the one quart starter and shook up the bucket good. Then I added the rest of the wort. The bucket was still a little low so I poured another half gallon in, without really stirring. I then checked the gravity by using a sanitized turkey baster to take some wort off the top. The gravity corrected for temp was 1.050. My question is, could the last half gallon of water diluted the top part of the wort, not mixing through the whole fermenter? With the wort gravity being heavier than water I can see how this is possible, or is it just wishful thinking?