I would recommend moving this logic to the script as create field/attribute with the same logic then use that field in the list box. It will provide more consistent results and also be useful in set analysis.
if(SERVICE_TIER = 'type1','type1',
IF(SERVICE_TIER = 'type2','type2',
IF(SERVICE_TIER = 'type3','type3','Internal'))) as Service_Tier_Type