[Groff] indentation in bibliographies

[Joerg van den Hoff]

I'm using 'refer' (and the ms macros) for generation of auto-numbered literature
references (using the refer 'bibliography' request).

problem: if numbers go beyond 99 there is not enough indentation space,
so I get something like

...
98. some reference
99. some reference
100.
   some reference
...


I therefore want to increase the indentation to get

...
98.  some reference
99.  some reference
100. some reference
...


but I cannot recall/find how to do this.
question: is there a number register to achieve this or how is it done?
e.g. modfiying PI seems to have no effect on this...

thanks

joerg