On the notes to MN 44
Venerable 
In the text, ‘sakkāya’ is defined as the five grasping aggregates. You say of the term ‘sakkāya’:
The commentaries define sakkāya as “the three planes of cyclic existence”, i.e. all that exists. Thus sakkāya is the “substantial reality” that is mistakenly assumed to be a “self”.
So ‘sakkāya’ is “all that exists” and the “substantial reality,” and it is defined as “the five grasping aggregates.”
Later on, you have a note on the aggregates which says:
In the suttas, the five aggregates are not presented as a catch-all category that encompasses all of reality
But I can’t help but feel that these two notes have some friction between them, as well as the translation which identifies the aggregates with “substantial reality.” Are the five aggregates the “reality” which is “all that exists,” or do they not capture “all of reality”?
I can only reconcile it if I take your note to mean that the Buddha has pragmatically reduced “all reality” to what people relate a self to, but that there are other things in reality which people don’t identify in relation to. Still though, I’m left feeling a bit unsure about the meaning of the notes and their relationship to the translations.
Aside: I just made a post here with some thoughts on this issue.