Halliday & Matthiessen (1999: 111-2):
The second consequence is that although the two variables, locution/idea and quoting/reporting, can combine in either of the two possible alignments, there is a natural default condition, which is that locution goes with quoting and idea goes with reporting, as shown in Figure 3-6.
The reason for this is clear where the first-order phenomenon is one of saying (prototypically shared semiosis), the projected figure can be presented as if it was also of the same order: Harriet said + "Shall I feed the cat?" (reversible as "Shall I feed the cat?" + said Harriet).
Where the first-order phenomenon is one of sensing (unshared semiosis), the projected figure has no counterpart on the first-order plane of experience and cannot be naturally presented as if it had; so, Harriet wondered + whether she should feed the cat.
But there is always the possibility of semogenic extension by cross-coupling; so we also find the corresponding marked alignments: locution/report Harriet asked + whether she should feed the cat, and idea/quote Harriet wondered + "Shall I feed the cat?" — the latter being again reversible. See Halliday (1985: Chapter 7) and Nesbitt & Plum (1988).