There are many threads on this, but I would personally recommend that you do not spend any energy thinking about LOAs. We can speculate what combination of factors may trigger a LOA to be generated, but very few of the forum members can provide an inside view to the process.
There are way too many other things within your sphere of control which should be a priority in the short term. Make sure your applications are ready and submitted to each MOC and nomination source, you have Plans B / C / D in place, stay in shape, keep your grades up, have have some fun (just stay out of trouble).