The building and exchanging gadgets both have a 'range' setting, that specifies the range of blocks affected. Each mode has a slightly different take on this, but in general this represents an area.
For example, in Horizontal Row mode a range of 3 will be 3 blocks total, 1 on each side of the block you're looking at. This is rounded if you choose an even number.
Range of 3
A range of 3
For walls, a range of 3 will build a 3x3 wall. Even numbers modify the height of the wall slightly.
Experiment with the preview to get the outcome you are looking for!
Range of 3
A range of 3