Unfortunately, there's no "setting" controlling XML output specific to the formatting of indicated tags. Its the nature of the XDocument library to output human formatted XML. As an experiment you can literally "flatten" each member tag section using a regex and add it back to the XDocument object. Upon writing that document back to a file, you will find your previously flattened xml all nicely formatted again.
public static void XdocumentFormatExperiment(string inputFilePath, string outputFilePath)
{
XDocument doc = XDocument.Load(inputFilePath);
foreach (var member in doc.Descendants("member").ToList())
{
// Convert the member element and its children to a single line string
string memberAsString = member.ToString();
string singleLineMember = Regex.Replace(memberAsString, @"\r\n?|\n", "");
singleLineMember = Regex.Replace(singleLineMember, @">\s*<", "><");
Console.WriteLine(singleLineMember); // all nicely flattened on one line...
// replace the original <member tag with the flattened one
member.ReplaceWith(XElement.Parse(singleLineMember));
}
//write out the new xml doc with the flattened member tags
// open the file and find they're all formatted again.
doc.Save(outputFilePath);
}