Part of the problem lies with ATSD requiring ATCOs to pedantically specify the Type Of Service before and after crossing CAS boundaries whether the ATSU is an ATSOCA Provider or not. Non-LARS Providers (eg Heathrow) are required to specify the Type Of Service on initial response so that the User will be in no doubt, eg.
"Clearance is....Basic Service outside CTR"
"Entering CTR, Radar Control Service"
"Leaving CTR, Service Terminates...."
consequently some Users perceive a need to request an ATSOCA from a CAS ATCU.