Ssl for saas on different backends

Hi,
I’m using ssl for saas with success for months now.
But I wanted to add a different backend and it looks it’s routed to the same server :

customer-domain CNAME on subdomain.my-domain → IP A works well

service.customer-domain CNAME on service.subdomain.my-domain → IP B does not work when proxified (goes to IP A)

is it something manageable on pro plan or there is only 1 destination (the specified backup origin server) ?

Thanks.