On 15 May, Heinrich received promotion to Feldzeugmeister and was appointed to command V Armeekorps. He missed the Battle of Aspern-Essling because his troops were detailed to watch the Nussdorf sector. By the orders of Archduke Charles, his small corps also sat out the Battle of Wagram. Instead, they guarded the Danube river crossings to the west of the battlefield. His 8,958 troops included the brigades of Johann Neustädter, Philipp Pfluger, and Johann Klebelsberg. On 10 July, Reuss held off the pursuing French army in a successful rearguard action at Schöngrabern. The following day, his corps participated in a much larger action at Znaim, where each side lost about 6,000 casualties. In the early hours of 12 July, both sides agreed to a cease fire. For the actions of 10–11 July, Heinrich received the Knight's Cross of the Military Order of Maria Theresa.