How to chose X point in harmonic pattern

For harmonic pattern, the most important and confused thing is how to chose the X point.

In this chart, due to Canadian rate decision, there are two candles with very long tails. The X I selected is based on it is the actual start point for the down trend. From there, we can find the potential butterfly pattern is in forming.

Please share your idea and comments. I am still new in forex trading.