Batch Size vs. FG - How are they affiliated?

When I adjust my batch size, my FG changes. I'm confused how these are related? Things that should affected my FG are mash temp, and yeast.

Can someone explain this to me?

How are you adjusting your batch size?  If you are doing this by just changing the batch size within a recipe and not scaling the recipe to a new batch size, then the grain bill does not change and the result is that you have the same amount of grains contributing a fixed amount of sugars to the wort.  The net result would be a dilution of the wort and therefore a reduced FG.

After I posted this I realized it was the increase in batch size only, not adjusting the grains, that would result in dilution of the FG.

Thanks