https://www.ibm.com/docs/en/ims/15.4.0?topic=parameters-recasz-parameter-procedures
IMS 15.4 - System definition - RECASZ= parameter for procedures
Use the RECASZ= parameter in procedure to specify a 1- to 5-digit number indicating the size of the receive-any buffers. Valid values are from 112 to 30720.
imssystemdefinitionparameterprocedures