The other field_types come about as a result of a combination of the bus syntax. For instance, you may combine field_type2 & field_type3 syntaxes and it'd still be valid bus syntax.

Maybe you'd want to expand the bus string into its individual signals first. Cadence already has a SKILL function to do this.

By the way, the expansions you have shown (with underscores) already have netlist name mappings performed so they can be taken into spectre without choking.

Make sure you take the *2 and *4 multipliers into account. The expansion will be the cross product of each bus's individual signals (multiplied or not).