How best to set Matlab Level 2 S-Function port sizes based on dialog parameters?

I'm creating a Level 2 S-Function with two inputs and one output port. One input port and one Output port will vary in size, but only based upon non-tunable dialog parameters. Note that the variable input and output ports will not be the same size.

I know I can set port sizes to variable in setup like this:

block.OutputPort(1).DimensionsMode = 'Variable';

Then later set the current dimensions like this:

block.OutputPort(1).Dimensions =[1, my_length_var];

but is this the best way in my case?

If it is, where is the best place to set the dimensions, e.g. in InitializeConditions?