I made this calculations:
On a floe 1m thick 10kmx10km:
One side: 10km long x 1 meter thick (0.001 km) = 0.01 km2
Because there are four similar sides: 0.01 km2
x 4 = 0.04 km2
Because it is only one floe: Total: 0.04 x 1 = 0.04 km2
Including the bottom face: 100.04 km2
, if 100% of the side faces are in contact with the water.
On the other hand, on 100 floes, 1m thick 1kmx1km:
One side: 1km long x 0.001 km thick = 0.001 km2
Because there are four similar sides: 0.001 km2
x 4 = 0.004 km2
Because there are 100 floes: Total: 0.004 x 100 = 0.4 km2
Including the bottom face: 100.4 km2
, if 100% the side faces are in contact with the water.
This is not counting the top face.
Sorry for my first comment.