What is the difference between the "Chief Acquisition Officer" v. the "Senior Procurement Executive"?

What is the difference between the Chief Acquisition Officer v. the Senior Procurement Executive? When I look at the definitions in FAR 2.101, it sounds like the CAO's role is to oversee the actual performance of the acquisition activities, while the SPE's role is to "manage the direction of the acquisition system/policies." However, I am aware that some agencies do follow this interpretation, others do not. Some agencies/Departments swap the roles, so there are SPEs who are not doing policy but overseeing the award and administration of contracts. The FAR 2.101 definitions refer to separate congressional laws, but I looked at those and did not find any further elucidation from them.

Can anyone shed light on this? I would like to hear others' experiences with this.