If frame overhead consideration is enabled, then queue scheduler accounts for the Ethernet frame overhead. The maximum egress bandwidth accounts for the Ethernet frame overhead (it accounts for the IFG (inter-frame gap) and the preamble). Typically, the IFG and preamble constitutes about 12 + 8 = 20 bytes. The overhead for Ethernet ports uses this value.
A configurable CLI command enables accounting of the frame overhead. This is a system wide parameter and affects the behavior of all egress queues (when frame-based-accounting is enabled on egress port (network ports or access-uplink ports, as applicable), the associated queues also account for frame overhead implicitly). When disabled, the egress-rate command does not account for the Ethernet frame overhead.