Please see the attached scene. The spaces are caused because each row in an A2S generator is calculated independently, so segments can not flow down to fill the gap. Instead the next segment in the left and right input is added only when a new row is created. To resolve this I've used used a compose operator to add two tiles on the sides for every row and then a Transform operators to adjust the Padding and Fixed Translation to move them into the correct position.
I hope that helps.