I got good results by deleting that file you said. Actually I just moved it and restarted NVDA. I don't know if the back quote is being passed to the synthesizer, but it seems to work without that file in the NVDA program folder.
Well this is because this file has some rules in it, for example two words written as one, but each word capitalized, should be treated as two separate words. But there are some advantages to this file not being there, like the better processing of speech tags like the ones in eloquence.
How about we just choose to pass the symbol to the synthesizer without deleting or having to rename/move this file every time we want the backquote voice tags enabled?
Yes, and there unfortunately is no way to change that. And in your case too, I think you either don't have the ` symbol passed to the synthesizer or you don't have the backquote voice tags enabled. In the former case, which I think is the more likely one, you know that symbol pronunciation dialog in the NVDA menu? This is where you can change that. Just search for "graav" in the filter.
Yes, I just had a look again. There is a part in that file "break words that have numbers at the end" and then the line: ((?:(?=\D)\w)+)(\d+) \1 \2 1 1
So, deleting that should be enough for correct processing of tags. I myself have reasons though for deleting that file with all of these rules.