With Solder from Tin, the pipe to ground recipe is pipes + solder. So when this mod removes the pipes from the recipe, its left a bit empty, with only 4 Solder, and nothing to actually solder together
In terms of tiles-per-pipe, it seems fair imho to make the recipe still take 2 pipes, since you get 2 tiles per pair of pipe to ground. So in this case the recipe would be 4 solder and 2 pipes.