Hi Matt,
In the entire Saxon Army, only one unit has got connexion with Reuss Principality of Reuss : the JB Nr. 13. For that we have to see if units has a Chef and who is he. For the Reuss, the unit is JB Nr. 13.
For example, if one Saxon officer received the Saxe Weimar knight cross of White Falcon, the probability he is from the Karabiner Regiment is high, like the Great Duke of Saxe Weimar was the Chef of that unit.
For your info, here is a photo of Freiherr von Uslar Gleichen, from JB Nr. 13. Note that he wore the Reuss 1st class cross with X.
Regards
Christophe