After the IP Datagram header has been added, the TCPIPSendICMP call only sends out the first two bytes of the target ICMP message, regardless of what value is given for the message length. As a result, it is impossible to send out a valid ICMP packet by this call.
Relevant source file is:
https://sourceforge.net/p/marinetti/code/HEAD/tree/trunk/MOSP/Marinetti/Init/I.ICMP.S#l102