Mark McG replied the topic: Core game - No Man's Land shelling procedure
I also use the first option.
The rule reads
"Starting with the row closest to enemy, one targeting die is rolled. Counting each hex, going left to right, place a crater on the hex of the number rolled. Roll the die again. Starting with the next hex in the row, count the hexes and place a crater on the hex of the number rolled. Repeat this procedure until the number rolled takes the count off the right side of the battlefield. Working toward the starting player, complete the same procedure for all rows indicated as No-Man’s-Land."
The last sentence leads me to think the process is row by row. The net effect I think is indifferent.