troubleshooting tail drops with CBWFQ

All,

I noticed a lot of tail drops in the CBWFQ service policy even when the
traffic is well below the shaping average and suspecting it is due to the
traffic being bursty and queue size is too small.. Can anybody suggest good
troubleshooting commands/instructions to confirm the facts.. Also, How do I
achieve /calculate optimum queue size for a given scenario

policy-map POL-PIR-24000
  class class-default
   shape average 24000000
   service-policy child-eigrp
!
policy-map child-eigrp
  class EIGRP
   bandwidth percent 5
  class class-default
   bandwidth percent 95

sh policy-map interface Gi0/3.1454
GigabitEthernet0/3.1454

  Service-policy output: POL-PIR-24000

    Class-map: class-default (match-any)
      3507361659 packets, 1331902377498 bytes
      5 minute offered rate 5820000 bps, drop rate 1444000 bps
      Match: any
      Traffic Shaping
           Target/Average Byte Sustain Excess Interval Increment
             Rate Limit bits/int bits/int (ms) (bytes)
         24000000/24000000 150000 600000 600000 25 75000

        Adapt Queue Packets Bytes Packets Bytes Shaping
        Active Depth Delayed Delayed Active
        - 0 3384657739 2059632195 237539998 61135324 no

      Service-policy : child-eigrp

        Class-map: EIGRP (match-any)
          2851680 packets, 337279531 bytes
          5 minute offered rate 0 bps, drop rate 0 bps
          Match: access-group name Seigrp
            2851680 packets, 337279531 bytes
            5 minute rate 0 bps
          Queueing
            Output Queue: Conversation 265
            Bandwidth 5 (%)
            Bandwidth 1200 (kbps) Max Threshold 64 (packets)
            (pkts matched/bytes matched) 25/3039
        (depth/total drops/no-buffer drops) 0/0/0

        Class-map: class-default (match-any)
          3504510053 packets, 1331565104583 bytes
          5 minute offered rate 5820000 bps, drop rate 1444000 bps
          Match: any
          Queueing
            Output Queue: Conversation 266
            Bandwidth 95 (%)
            Bandwidth 22800 (kbps) Max Threshold 64 (packets)
            (pkts matched/bytes matched) 360229491/372124665094
        (depth/total drops/no-buffer drops) 0/122704071/0

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Received on Thu Jun 23 2011 - 15:27:27 ART