When I install K2 blackpearl for SharePoint 2013 for any SharePoint 2013 subsite under the same parent site, I notice that a unique app domain is created for each subsite, as follows:

https://app-51330ed143e498 for subsite 1

https://app-51330ed143e497 for subsite 2

https://app-51330ed143e49f for subsite 3

My understanding was that the same domain would be used for each K2 app install, as long as the subsite was created underneath the same parent site, but it looks like I'm wrong.  So, my question is: Is there any way a single domain can be used for each K2 app install for , or does each K2 app install require a unique domain, even though the subsites are under the same parent url?