Phil,
my experience with HK parrels matches well with yours. I have found that the higher the aspect ratio of the sail, the lower is the load on (or need for) the HK parrels.
It is no surprise that these parrels mainly were spotted on Hong Kong junks: Their mainsails were of extreme low-aspect ratio and with just about no sail forward of the mast. These sails were in other words desperately unbalanced, and the upward bend observed in their battens clearly indicates that the HK-parrels were struggling.
I have often observed on my junks that when the sail is sheeted out for running, then one or more HK parrels go slack. To me it seems that the HK parrels are mainly needed when close-hauled. This is when the sheetlets try their best to haul the battens out of the sail. On Ingeborg I took care to use a quite stout and low-stretch rope for the HK-parrels. That has paid off and I mostly avoid diagonal creases, in one direction or the other.
Arne
PS 20230822 I let you have this great photo of Brenda B, which popped up on Facebook today.
![](/resources/photo/uTljNHN_T9II2VPclRSi4daFTXCMNY1QvvWviokLABo_RROQYknFtWtCuTfWJD3LnRYHMBpFIB7orrxVHykRnQ2/preview)
(Photo section 8 in my member's album)