\begin{luacode}
local adjacc = function (char,adj)
char["top_accent"] = adj*char["width"]
end
local patch_stixmath = function (fontdata)
if fontdata.psname == "STIXTwoMath"
then
adjacc(fontdata.characters[119907],.55)
adjacc(fontdata.characters[119908],.55)
end
end
luatexbase.add_to_callback
(
"luaotfload.patch_font",
patch_stixmath,
"change_stixmath"
)
\end{luacode}