A chiseled block with a liquid placed in it makes it a “liquid block”. In this case
One lava block if it flows down from it source its technically making a cross pattern.
Black source
Red flowing (down)
In the case of lava the flow blocks are the blocks that burn plus the blocks under neath “flow”.
In your shot you have a square of 2x2 blocks and one source block in the chisel part. (Game sees this as a flat surface).
If you place lava normally on a flat block surface it flows out. It is 3,5 blocks so say 4 from source creating this pattern from top view.
Because the chiseled area is
Is viewed as a flat surface the lava flows “off the edges” in a way of speaking.
In this case orange is the flowing lava (in the chiseled area) contained. Yes but the “drop flow” can only be stopped with a full block next and underneath it (this bock may be chiseled but has to be in a way that it blocks the flow). This has to be a non burnable block like stone, metal, glass… organic blocks will burn in the red area.