Can’t help with the document you are looking for .
what I can say is that the mode 5 is desensitised below 150agl .
Below 150 feet you would need to be 3.5 dots low to get just a soft warning .4 dots low to get a hard warning .
so based on this , if said pilot was getting warnings below 100feet , he was seriously low and seriously in danger , so I would say your safety manager has a point .
if there were no warnings below 100 feet , then all good for me , irrespective of the GS deviation on the instruments.