Setting the Sortable property of a Managed Property in Sharepoint 2013

I have a set of Management Properties that are being automatically created from a Site Collecttion in Search in SP2013, but the Searchable and Sortable properties are not set. 

I have managed to set the Searchable property using a powershell via

Set-SPEnterpriseSearchMetaDataManagedProperty -SearchApplication$ssa-Identity "propname"-FullTextQueriable$true

But I cannot work out how or where to set the Sortable attribute.. Can this be set via powershell?