The following article contains an answer for the question: What part of the church did Nikolova consider unsuitable for the baptism? , can you please find it? 

The rectangular narthex constitutes the middle part of the building, between the atrium and the cella, and serves as the lobby of the church. It lies directly east of the atrium, through a wide gate flanked by a couple of high circular turrets. Mavrodinov likens the narthex of the Round Church to similar structures in the churches of Mount Athos, because of its depth.Together with the north and south wall, the entrance of the narthex effectively isolates two smaller parts of the atrium, similar in plan and accessible through doors. The north part includes a small necropolis, while the south part was probably a baptistery, as it features a square installation with a clay pipe that resembles a baptismal font. However, Nikolova considers its shape much too unusual and its depth unsuitable for baptism, and believes it may instead have been designed as a vessel for dispensing holy water.Measuring 5 m × 9.50 m (16.4 ft × 31.2 ft), the narthex is the part of the Round Church which has survived in best shape, as some of its walls reach 3 m (9.8 ft). Its two turrets have a diameter of 3.20 m (10.5 ft); each has an entrance facing the interior of the narthex and three windows. The higher reaches of the towers were reached via spiral stairways, archaeological remains of which have been unearthed in the north turret. There are two pairs of columns inside the narthex, supporting its second floor, which is accessible from the north tower. The columns divide the narthex into three naves and mark the way from the narthex entrance to the gates of the rotunda.

the south part