how calculation engine compute from different dimension intersections

For example, I have a three measures X, Y, Z

X base intx: a_b

Y base intx: a_b_c

Z base intx: b_c

expression: X = f(Y, Z)

1) how the engine process the source and destination measures with different intersection?

in my opinion, first aligns all source measures' intx with destination.

Eg.

aggregates Y's dimension "c" to bottom level as per its "Default Agg" definition;

aggregates Z's dimension "c" to bottom level as per its "Default Agg", and then simply add dimension "a" to Z

Please correct me if the process is wrong.

Is there any document about different intersection calculation?