Answer
The truncation isn't a storage limitation — the underlying custom field data type (NUMBER) comfortably supports many more decimal places than 2. The actual cause is the field's chosen formatting option: setting the field's format to 'Decimal' is specifically what causes the client to truncate entry and storage to 2 decimal places. Switching the field's format to 'Unformatted' instead allows entering (and correctly storing) numbers with well beyond 2 decimal places — it's the display/entry formatting choice that's constraining precision, not the underlying column type.