I have a similar desk. It works fine. It is not identical to yours, so make sure to check your dimensions.
But…
As long as the clamps will attach to the desk fully, you are sound.
There really is no structural reason to be completely flush with the desk. It will secure as soundly in either case. It will just stick out from the table a bit if you don’t line it up with the mount.
Now, if you don’t have room for the clamps, you’ll need the extension.
The tan strip of particleboard is the table, you can see the mount extends well in front of that. I may be able to get these flush with my table but I never bothered.
It does pull the weight out from the table a little, so I suppose it could make certain tables easier to tip. But it clamps!