LWA,
Using 40 units isn't excessive as long as it control your blood glucose, much tripe is written about insulin usage, but we are all different and our bodies have different requirements, so please don't feel like a failure if your insulin usage is more than the next persons.
The only way of knowing if you have the split dose correctlyis by fasting, this will mean skipping a meal and testing bg throughout this period, provided your previous meal has been bolused correctly you should see if your background insulin is sufficient by your meter results. So, if your bg rises increase your levemir by 2 units, should it fall and cause hypo's then you need to reduce it by the same, if in doubt ask your dsn for guidance.
Nigel