When garbage rows are sent your way, they sometimes have the gap in the same place, allowing you to clear up to four rows at once with a single line piece. Other times however, the gaps are scattered in different places, meaning you have to clear the rows one after the other to carve your way down.
When does this happen? Can I somehow influence the garbage rows to have the gap at the same place? Or is this just the result of a single player sending me all their garbage?