Defined capacity is an optional LPAR setting. If you establish a defined capacity in an LPAR, z/OS workload management (WLM) monitors the four-hour rolling average utilization of that LPAR. If the four-hour rolling average utilization of the LPAR exceeds the defined capacity, the LPAR is temporarily capped (this is called soft capping) until the four-hour rolling average drops back below the defined capacity.
See IBM for details.
Does CA honor soft cap for CA TPX software?
CA TPX for z/OS
From a product perspective, if you have a valid LMP key then TPX will execute. Soft cap not a consideration.
This question is actually a pricing question and you should contact your CA account team for specific pricing and any licensing implications.
IBM Implications of a defined capacity