I would argue that 30s intervals are not vo2 max but thats besides the point.
For any vo2 max intervals I dont use erg as they are supposed to be maximal and set % of FTP does not really work across everyone for power >FTP.
I would do them in resistance mode and pace as hard as you can while maintaining the same watts throughout the interval and across them.
Ignoring the iLevels stuff you can see here that there is significant variation in PDC at shorter efforts.
I would also aim for higher cadence efforts at the expense of maximal power but thats another topic that has been covered here.