A Yantra is not just the residing seat of a devatA; it is the devatA itself. It is not just a representation, or a copy. It is not a substitute for the devatA. It is the devatA itself. It is the presentation of the devatA and
not a re-presentation. More so in the case of ambaal.
For, Her Divine Presence is very special in Her Yantra. It is because of this that ambaalpUjA is mostly done to Her Yantra than to Her most beautiful physical form.