https://community.adobe.com/feature-requests-530/allow-texttotal-to-work-in-the-range-selector-start-end-offset-1215056
Allow textTotal to work in the Range Selector (Start,End & Offset) | Community
And it should work for both Percentage/index Units.A N D if it can work in the text.sourceText prop, this will be a bonus.
to work inthe range