With NPCDialogWnd.uc modification of Interface.u you can change the size of the window for each HTML:
Use this: https://pastebin.com/iYs8AQQ7
and you will need also this one on UICommonAPI.uc::
function String StringBetween(String param, String iString1, String iString2)
{
local int varInt;
varInt = InStr(param, iString1) + Len(iString1);
return Mid(param, varInt, InStr(param, iString2) - varInt);
}
Inside the <html> tag you can add "WIDTH=X", "HEIGHT=X" or "IMAGE=X"