The only fonts I know that have more than one "large" version of the math operators are Asana Math and Cambria Math. The other ones just have one glyph for the
\textstyle version and other for the
This causes problems. It seems that similar problems also happen with Cambria; their
\displaystyle summation operator is too large.
So, what's the use of having them? Does LuaTeX uses them in some way? Does MS Word? Is it even possible to access them from within LuaTeX? (This technique does not seem to work for them - or in fact for most math operators).