On 13 April, the German objective was the Servia Pass. They wanted to cut through Grevena outflank the Aliakmon position "from the west". You had the 9th Armored Division moved through Kozani and patrol-sized units had crossed the Aliakmon river. That had happened as early as 14 April.
The German assessment was that the 6th and 7th Australian Divisions and the New Zealand Division were "in full retreat", along with the 2nd British Armoured Division. They saw the British movements as being "withdrawal moves".
The 11th German Infantry Regiment staged an attack at Servia. Their losses were limited to "36 killed, 72 wounded, and 190 missing". It was the Adolf Hitler Division that had arrived at the "Kastoria-Grevena" road. They had blocked the supply line for the Greek army that was pulling out of Albania.
The German 73rd Division was sent to protect the "40 Corps flank". The Germans thought that the Greek army was still fighting well. In fact, though, the Greek army commander had abandoned his troops.
The German mountain corps that had been at Salonika on 9 April were to attack Edessa Pass, but the situation was fluid and in fact the attack was unnecessary. This is based on the account in "Greece, Crete, and Syria" by Gavin Long.