Consider below scenario to understand calculated field intelligence logic.
1. I have created custom field called lookup and relate to system entity called ‘Unit’ with named ‘new_uomid’.
2. Created new custom field as string (Calculated) and tried to set action (Calculated field) with lookup value as ‘new_uomid’. I have added dot after ‘new_uomid’ field to get intellisense but it did not appears.
3. Then , I have created new custom field called lookup and relate to system entity called ‘Account’ with named ‘new_accountid’
4. Open existing string field and tried to set action (Calculated field) with lookup value ‘new_accountid’, then I have added dot to get intelligence and it is working properly.
Reason : Each entity have metadata property called ‘IsValidForAdvancedFind’. If this properly is true then only you will get intellisense option in calculated field for selected entity. In simple words if entity is visible in advanced filed view then you will get intellisense option in calculated field.