I'll have to try Methods A and B again as well. They have a very basic video on retouching on their site for an application that is not what I'm experiencing and your description provides nice details. Sometimes this works, sometimes it simply won't let you retouch from the other version. I find it sometimes helps to redo one or other or both of the stacks to get the other one to appear in the drop-down list. It doesn't always let you do this - sometimes the stack you want to use isn't in the drop-down list. You use the Use another output as a source drop-down list when in Retouching to get to the other stack that you want to paint with. As with much else, it depends on the particular image. In that case you may be able to go right up to and slightly over the edge, although to be honest that last little bit of painting from Method C right at the edge may not make much or any visible difference.

60%, but it varies depending on the image), especially with images like this one with very different colours between the subject and the background. It can help to set the retouching Color Tolerance parameter lower than 100% (e.g. I often use both method B and Method C and use Helicon Focus' retouching to use the Method B version as the base and then paint over the subject using the Method C version, avoiding the very edges. I often get halos like that when using Method C where the edge of the subject is against a plain background.

Maybe that is part of the problem? Something else? The Helicon tutorial videos don't address this issue, so will have to do some trial and error, I suppose. I have the focus increment set to the lowest setting. Just started using an R5 to bracket photos and ended up with a LOT of shots in the stack (which may be the problem) and seeing a halo type artifact around images stacked with Helicon Focus (attached).

Helicon focus tutorials