\input{luaotfload.sty}
\directlua {
  local function patch_font(fontdata)
    local mc = fontdata.MathConstants
    local em = fontdata.units
    local sz = fontdata.size
    if fontdata.psname == "CambriaMath" and mc then
      mc.DisplayOperatorMinHeight = 2800 / em * sz
    end
  end
 luaotfload.add_patch_callback(patch_font, "modernmath.patch_font")
}

\font\4={name:Cambria Math:mode=base;script=math} at 10pt
\font\5={name:Cambria Math:mode=base;script=math;ssty=1} at 7pt
\font\6={name:Cambria Math:mode=node;script=math;ssty=2} at 5pt
\textfont4=\4 \scriptfont4=\5 \scriptscriptfont4=\6

$$
\Umathchar"1"4`∫
\Umathchar"1"4`∑
$$
\bye