I think probably AccessControl is setting the control from the data. On a new record, the data will be “”.
One way to get a default in an Access is to rename the field (in the query) e.g. to sT_Type_default and then to create Rule_sT_Type_default which is simply function () { return ‘Long’ }
(It is possible to put the rule on the actual field name, but this can be confusing so it is better to rename.)