I used a 'stacked' kite set up and a land board in 96.
some British backpackers stayed with my family and had 4 ram air brake line kites. From memory each kite was the same size around 2m with a single 4.5mm graphite rod running through the leading edge. The main lines were 20m and the spacer lines for stacking were around 2m-2.5m.
in 10-12knots of wind they stacked 3 to make land boarding possible. It was a really sluggish set up, but it worked. Using it, I only remember watching a delayed turning response from the first to the second to the third. It was much more fun in 18knts+ with one.
my guess is- if you stack kites- It just adds together the bar pressure of each, less line stretch between the top and bottom canopies when the top one starts to lead the other. Line stretch then becomes a delay in a correction to the top kite.