Red Bull ran at the initial Jerez and Barcelona tests - and then the two opening days of the final Barcelona test - with its own solution in the wake of the FIA's blown exhaust clampdown.
"We had a nice surprise on the penultimate day (of winter testing)," Sauber team boss Peter Sauber wrote in his column for Sonntagsblick newspaper.
"Red Bull announced their plans to use a heavily modified car, as it will race in Melbourne.
"Compared to their first version it had a completely different rear, which differs significantly from most cars -- but not ours.
"The Red Bull and our C31 have a very similar concept, concerning the management of the airflow at the rear.
"For our engineers, it was an extra confirmation that they have chosen the right development direction. They are convinced that this concept has the potential for further development," added Sauber.