As far as I know, there is no way of changing the reaction on the auto-level struts. The only adjustmnet I have had performed in my previous W123 300TD and W124 300TE was in the kick-in weight sensor for the system to start working. I beleive the system remains off up to 250/300 pounds of added weight, after that the systems begins to work.
The dealer adjusted the auto-levelling device to start working only after 500/550 pounds were added, in this way I could board up to three rear seating passengers without having it to work at all times.
From many replies I have read in this site and from my own personal experience with wagons for 18 years they definitely tend to ride much harder than the equivalent sedans. They also have an inherent "boom" echo created by road noise. I understand the W210 wagon particuliarly rides much firmer than the sedan, unlike the W123 and W124 which came close to the sedan counterparts.
The tires are a very important issue. My E320T change its behavior completely (ride, handling, etc) after I changed from a set of BFGoodrich Touring tires to a set of High Performance Pirellis.