Look in Section VIII, Appendix 4. In the terminology section, tungsten is included with other rounded indications and graded as such since it is not linear. Rounded indications are graded in UW-51 but are not a factor when using UW-52.
Remember, indications with a maximum length of three times the width or less are "rounded". Tails can change this defination and force you into a linear situation for evaluation.