Thanks, that worked, but using the same class number in the filetype.xml file, like this:-
<class name="253" type="rar,gzip,zip,gz,jpg,jpeg,png,gif,bmp,pdf" maxupload="3M" />
<class name="253" type="iar" maxupload="20M" />
<class name="253" type="oar" maxupload="500M" />
When I created this question, I was following directions on the github:-
Which showed the use of class numbers and without any explanation of their meanings, I assumed the numbers were a type of category, but it also said to not use duplicate classes, which also confused the situation, but now I have it clear, I used the same class (253) for multiple filetypes with differing upload size restrictions, which works perfectly now.
Looking at the date on that github page, I noticed it's 2017, it might be a good idea to update it for E107 V2 bootstrap.
This ticket can now be considered fix and closed.
Thanks for the help.