Of course, there are different views on this subject and they all have their justification. Everyone plays CM a little differently.
For me personally, the direct interception of enemy units in the reinforcement zone has little to do with fun. The reinforcement is teleported directly onto the battlefield and is then free to be shot down. There is no way to avoid this situation. The principle is the same as with pre-planned artillery in small setup zones.
Since I haven't played for a very long time, I would just like to know whether this procedure (intercepting enemy units directly in the reinforcement zone) is a permissible practice?
If so, I wouldn't be in SoM January after all, as the above approach is possible in the RT scenario.
I think it's always better to address such issues beforehand. Saves time and spares your nerves