Service Level Agreements do not support inheritance from base tables to extended tables
When you define a Service Level Agreement, you specify the task table, or the specific table extended from the task, to which it applies, for example, Incident (incident), Problem (problem), Change Request (change_request), Request (sc_request), and so on.
Regardless of the version of the SLA Engine being used, each engine queries for only those SLA Definitions (contract_sla records) that apply to the Task Type being evaluated. The queries do not check for SLA Definitions that are defined on a base level in the table hierarchy.
If you have some type of SLA to apply to every task record in your instance regardless of the task type, you still must specify an SLA Definition for each task type. You cannot specify a single definition on the task table and have it apply everywhere.