Honestly, I don't quite understand it myself. And I had a boy already! You just learn to move quickly! Really.
Unfold & set out the new dipe underneath the baby, undo old dipe, wipe w/ a wipe, set aside old old dipe, do up new dipe. If any spray occurs cover quickly, usually it's when you undo old dipe & cool air hits 'em, just quickly recover w/ old dipe. And really if it's just pee, you learn to clean up & move on. Poop requires more cleaning.
DH & I *still* laugh when we remember the learning curve having to do with "move quickly." Two words --- projectile poop. DS was tiny, not home long, less than 2 weeks, we were still learning. We were changing a poopy diaper, on his changing table, which was then next to our bed. His butt was facing our bed. First mistake. While he was 1/2 naked, he had well, projectile poop. Sent both DH & I diving out of the way. DH said it was like something out of the Matrix, with poop just barely missing my head, while I moved seemingly in slow motion. Poop sprayed our bed, sheets, pillows, cover. We just burst out laughing, it was hysterical. Of course we had to strip the bed & do a whole bunch of laundry, but yeah, after that incident, we learned to move quickly.....