Rig Onsite and the Unit is Bigger than I Expected

we are in a pool that has 324 acreas, i went by the drilling site yesterday, there was no one in site it didnt have the name of the well, but it had the name of the owner and next to it, it had 900acreas. Why would 324 acreas turn into 900 acreas. Why do some drills sites have so much acreage and other take so little acreage?

Units are different sizes for a whole host of reasons, Different geology, different financial backing (horizontal drilling is expensive), able to secure more economic leases in certain areas, etc.