Hmmmm..... 1M tip was my first thought but you said you already have it.
In order to build up the icing into the nice mound, it works best to start from the outside and work in, using each row of icing as a base to build up higher and higher into a peak. Not sure if I am describing this welll...can anyone else help?
serenelui - when you were using the 1M tip, how were you putting it on the cupcake? Maybe if we know what you were doing that didn't give you the results you wanted, we can help give some hints to make it work better for you.