How does the Divine Tempest’s Psychoclasm rule interact if it destroys a mantlet?

" **Psychoclasm**: If this model destroys an enemy model with an attack with this weapon, this model can spike to allow you to replace the destroyed model with a small or medium-based solo from your reserves."

A mantlet is a model, but it doesn’t have a base size as per Thousand Worlds pg. 191:

“Mantlets are not units or warrior models and cannot be charged. They cannot attack, do not activate, and are not on bases. Mantets cannot move or be moved.”

A replaced model must be completely within the area of the larger of the two bases being replaced Thousand Worlds pg. 199:

“When replacing one model with another, place the new model so the area covered by the smaller of their bases is completely within the area covered by the larger. If the two bases are the same size, place the new model in the same location as the one being replaced. There must be room for the model’s base in the location the model is placed or you cannot place it there.”

What is the area covered by a mantlet if it doesn’t have a base size?