The amount of the total mash wouldn't matter, just the ratio. For example, if I made a mash with 1lb of grain and 1.5qt of water, I should run off about 1.080 (1.5qt/lb). If instead I did 10 times that, so 10lb of grain and 15qt of water, I should get the same thing since the ratio is the same.
Maybe think of it like you have a fixed amount of sugar, and you are diluting it in varying amounts of water. That isn't exactly true since I think the extraction rate changes with the grain/water ratio, but as a conceptual tool I think it works. So, if you dilute 40 gravity points of sugar (about a pound) in 4qt, your runnings would be 1.040. If you instead used 2qts, your runnings would be 1.080. Same amount of sugar, just less diluted.
Sorry if that wasn't helpful at all.