Yes, reply from “y not” is correct.
Big square = empty because both nirāmisa vedanā and samphassa-jā-vedanā are mind made, they originates in mind. Hence, those three types of nirāmisa and three types of samphassa-jā-vēdanā belongs to dhammā indriya only.
Up and down arrows in bhava section denotes range of indriya.
In kama loka = all vēdanā are possible in kama loka, as all senses are available.
In Rupa loka = only eye, ear and dhammā indriya available, hence, number of vedanā reduced.
Again in Arupa loka = only dhammā indriya is there.
Also, all vipakā vedanā except those originating from body/touch are strictly neutral in beginning. However, vipakā vedanā originating from body might be of three types: sukha (pleasent; example: experiencing cool winds in summer), dukha (unpleasant; Example: Experiencing heat in summer, having bodily illness of various types), adukha adukha vedanā (neutral; example. Just seating on chair for some short time.).
Hence, the up down arrows under vipakā vedanā.
Please comment if you have any further questions.