reducing surface area of a desalination system will reduce the energy losses and as a consequence increase the amount of distilled water. but by just reducing the surface area, we can not achieve a"High Efficiency System"! there are lots of other parameters are involved that can affect the efficiency of a solar desalination system more than just surface area.
The most eminent drawback of practical solar energy systems is the requirement of large area of the device since the solar irradiance per unit area is quite low. Reducing the dimensions of the device will reduce the collection and consequently the output will be low.
To increase the yield of a solar still its better to couple it with some solar collector. This will enhance the yield to several times.