Yes, except the number 16 is member dependent. One slot is used for the call proper, including its address offset (or function pointer position on the belt), a count of the expected number of results if more than one, and so on. There can be three belt numbers per slot, so any not needed for this are available for arguments. If there are still arguments then they are spread over additional slots, each of which get the same three belt numbers plus 32 bits of manifest that is also used for belt numbers.
If a belt number is 4 bits (common in members), and the first slot is completely used for administrivia, then the ganged slots add 11 more arguments each (three morsels plus 8×4 bits). However, it is not meaningfull to pass more atguments than the callee has belt. A 4-bit belt number means the belt is 16 long, so at worst needs two slots for arguments and three in all for the maximal argument list.
Similar reasoning determines the number of slots needed for other belt lengths. We currently have belt lengths of 8 and 32 defined as well as 16; it’s not clear whether a belt length of 64 is ever needed in a practical chip..