A mourner, during the first 7 days sits on a low chair. The mourner also generally does not leave the house. One exception would be if there is no minyan that can be set up in the mourner's house, so the mourner must go elsewhere.
In that case, and if the mourner does not serve as the shaliach tzibbur, when he sits for parts of the weekday shacharit davening, must he sit in a low chair? I guess the same question would apply at a minyan in his own home if he was not leading services but I wonder if there is a difference between "at home in a shiva minyan" and elsewhere which is not a shiva minyan per se.