Comp Time vs. Credit Hours

I would like to better understand the differences between the two types of Premium Hours. What are the rules dictating how credit hours and comp time are earned, accumulated and used? What are the relative advantages and disadvantages for each?

Comp Time and LEAP

I had a situation where a LEAP (Law Enforcement Availability Pay) employee worked 5 hours past his regular shift. I want to authorize him three hours for comp time, 2 hours for LEAP pay, but my supervisor said it should be all LEAP pay. What is the correct way to pay this employee?

Comp Time/Overtime and the Pay Cap

I am a GS-15 Step 10. My Personnel Department reportedly has received direction from OPM that I cannot receive comp time because my salary restricts me from receiving overtime pay. I thought the agency could restrict the conversion of comp time to overtime pay but they do not accept that. Can you clarify for me?