You are right...it is only the space availability in the CDs because of which the artist has rendered Tanam for only 2 of the krithis.Otherwise the krithis are rendered with elaborate alapana, thanam (with Mridangam) and nereval, with kalpana swarams and thani @ Navarathri Mandapam at Trivandrum during the Navarathri restival.
VMR