Halliday & Matthiessen (2014: 275):
As far as tense is concerned, since a quality is typically the outcome of a preceding event, the same phenomenon will appear in present tense if represented as an Attribute but in past tense if represented as a Process in a ‘mental’ clause: for example, he’s frightened (present) is likely to be ‘relational attributive’, with the agnate ‘mental’ clause being (past in present) he’s been frightened.