Problem with big ship welder array welding small ship blocks

[Fingercolt]

It seems the big ship welder doesn´t weld a whole big grid?! Does it? Whenever i try to weld e.g. a small armor block 8x8 cube, some blocks of the cube, which are on the same height as the flattened corners of the big welders, are missing (not being welded by the quite lare big ship welder array)

Are the flattened corners of the big ship welder the borders for the welding "space" or does the block weld a whole large 1x1 grid(block)

i hope someone can help...;)