Stephen
I have also experimented with the Merge to HDR command with different RAW conversions and goyt the same message.
I've come to the conclusion that you actually need to take shots at different exposures although I haven't tried it.
There is one particulat shot that I have taken at Westonbirt which is very contrasty and so
I've never been able to get a result that I've been happy with.
Westonbirt 2295 -0.5 exp.jpg
To retain the highlight detail it needs a 3 stop under exposure on conversion from RAW
so I was very interested to try your 32 bit conversion technique and got this result which, I think, is a huge improvement.
Westonbirt 2295 HDP conv.jpg
When working through the conversion it occured to me that what this was effectively doing was applying quite a severe
levels & curves adjustment, so I went back to the 3 stop under conversion in 16 bit and had a go with levels and curves
and came up with this result.
Westonbirt 2295 lev & curv.jpg
What ever the way of getting there, thank you for giving me the impetus to go back to this image and have another go