Are you booting the target machine to DOS or WinPE ?
If you are using DOS, try using the FreeDOS equivalent of the classic DOS HIMEM.SYS extension. That utility understands the relatively new ACPI data table BIOS API introduced in the Windows 95 era, which is the only BIOS API that works properly in some machines. This then makes the results of that one working API available to Ghost's DOS extender via the XMS API, and so running the FreeDOS HIMEM.EXE will let Ghost use a great deal more of the installed memory than a mere 16Mb.
Unfortunately because FreeDOS is not licensed cleanly it can't be bundled or redistributed by Symantec alongside Ghost, but it's easy enough to obtain this tool by itself and include it in the PC-DOS templates used by the Ghost Boot Wizard, since it does work as a drop-in replacement for the IBM one.
However, I would recommend moving to WinPE if you are using DOS, as WinPE is much more compatible with modern hardware.