I have now done some testing with 3 versions of the same picture, one with AMAZE only, one with VNG4 only and one with both with the contrast slider on the demosaic setting set at 14. The split of areas that used AMAZE vs VNG matched the contrast mask when the contrast mask setting for capture sharpening was set at 28. I also did a dual demosaic at 28 and the areas matched the capture sharpening mask set at 56.
My method now is to decide which areas I want to use AMAZE and which to use VNG and set the demosaic method to VNG. I then enable capture sharpening and the contrast mask set the slider to 200 and bring it back down until everything I want in AMAZE is white. I make a note of the value and then halve it. I select the dual mosaic and use that halved value as the value for the contrast level there. I then recheck the mask and make sure the correct areas are all white where they should be and black where they should be. I adjust the capture sharpening contrast until things are OK and not the level. I then put half that level in the demosaic contrast box, etc. (usually only the one adjustment is needed).
Having got the demosaicing where it should be I then use the contrast mask for capture sharpening to sharpen the areas I want. As it happens that is usually lower than the split of areas that I want to use for the different demosaicers, as I want to sharpen some areas where I am using VNG4, so the two figures may end up close, but not usually the same.