Request type icons not showing for JSD Customer

We’re trying to display Request type icons for JSD customers using the icon links provided for request types by the following API endpoints:

GET /rest/servicedeskapi/servicedesk/{serviceDeskId}/requesttype
GET /rest/servicedeskapi/servicedesk/{serviceDeskId}/requesttype/{requestTypeId}
GET /rest/servicedeskapi/request (where requestType is expanded)
GET /rest/servicedeskapi/request/{issueIdOrKey} (where requestType is expanded)

The icon urls returned from these endpoints are on the form:
https://XXX.atlassian.net/secure/viewavatar?avatarType=SD_REQTYPE&avatarId=YYY&size=ZZZ

These urls seem to work fine, but not for the case where custom request type icons are used and a JSD customer is the one viewing the icon. In this case one of the default icons (the computer screen) is returned instead of the expected one.

Is there a way to avoid this issue? Could JSD customers also be allowed to access the correct icons?