Multistage or cascade lifters were first designed & demonstrated by my 3 stage cascade triangular lifter shown below. The aim of this design was to use a second EHD thrusting level underneath the first stage, as to continue to accelerate the neutral air molecules imparted from the first (top) level thruster. This design was further on successfully replicated by others and shows that surface area can be reduced by vertical stacking.
Three vertically cascaded basic lifter cells, with paper cones at corners for loading. This lifter weighs 3 to 4g, and lifts 5g additonal weight (including weight of paper cones). Top wire and middle foil are positive, top and bottom foils are negative. Connecting wires between foils should have enough clearance from the foil in between. I used a balsa piece as a standoff (2 of them).
Three vertically cascaded lifter flying. Pieces of wire weighing 0.5g each are put in the paper cones. The vertical support on the left took fire during one of the flights, that's why it's not there!