ASVT is being allocated over the 16MB line(31 bit address).
IBM has included this option in release 3.1.0 of the z/OS operating system where the ASVT address can be loaded as 31 bit or 24 bit.
This value (CBLOC VIRTUAL31(IHAASVT)) is set in the SYS1.PARMLIB(DIAGxx) member.
File Master Plus for IMS, release 12
z/OS 3.1 and the ASVT parameter
File Master Plus for IMS is not affected based on the ASVT parameter setting.