Custom Browse Main Artist Sort

I have created a Main Artists menu under Custom Browse and it sorts artist names containing non-English characters in a different order to the standard Artists menu. The Artists menu sorts as though the non-English characters were English characters. The Main Artists menu sorts in the UTF-8 table order. For example Artists menu gives
Joanne Hogg
João Gilberto
Jörgen van Rijen
José Feliciano
Joss Stone
which is what I want, while Main Artists gives
Joanne Hogg
Joss Stone
José Feliciano
João Gilberto
Jörgen van Rijen
This is on both LMS 7.6.6 and 7.9.1. I am not competent in XML to be able to customize the Main Artists sort order. Is there a setting to do this?