You need a different wrench. Check out the ones from Park Tools, they make a very thin but strong wrench in 36mm that is designed to specifically fit in the small space below the locknut.

Your thought pattern was correct when you bought the wrench you obtained but it is not quite suitable for your needs. You should check into returning it our keep it use on the locknut...but you will need a thinner wrench like I recommend above for the adjustable cup.

Good luck.
-j