Yes, there is a reason ;-)
The properties section is not pure executable code. Each statement of the property section defines an additional variable, with an optional initialization.
You have some options:
- you can construct an expression that returns an appropriate 3D array, using cat(3) and zeros()
- you can define a static method or a private/ function that returns the appropriate value and call the method or function in the initialization section
- you can leave the value uninitialized there, but initialize it in the constructor function
