20 seems me quite long, and in any case too long for netbios... and also for 'groupadd' and 'useradd', which have a limit to 16 chars.
But I see no reason for the 12 chars restriction, I have W95 clients allowing up to 15, so is it a W3.11 issue

?
But it's always possible, for fine tuning to follow that procedure :
/sbin/e-smith/db configuration set whatyouwannachange 15
/sbin/e-smith/signal-event console-save
where whatyouwannachange could be maxIbayNameLength, maxAcctNameLength or maxGroupNameLength.
one pint to help to swallow my bad English

!