The ping packet has a payload (the size of the payload depends on what you specify for the packet size) and one of the extended commands gives you the ability to specify what the payload will be - by default it is hex values of ABCD. If you select validate reply data it will check the response packet to verify that the payload received is an exact match for the payload sent out.
If you specify the datagram size to be 4000 and then you sweep it will generate data up to the size that you specify in the sweep. And when the datagram gets to the interface it will be fragmented into packets that will fit the frame size of the interface.
Without doing more investigation (packet capture, or packet debug, etc) I do not know how you would determine exactly which packets are being dropped.
HTH
Rick
HTH
Rick