covergroup cg1;
req_to_ack_cycles: coverpoint {req_to_ack_cycles[0], req_to_ack_cycles[1], req_to_ack_cycles[2], req_to_ack_cycles[3]}
endgroup: cg1
May be above would work.
covergroup cg1;
req_to_ack_cycles: coverpoint {req_to_ack_cycles[0], req_to_ack_cycles[1], req_to_ack_cycles[2], req_to_ack_cycles[3]}
endgroup: cg1
May be above would work.