Fence rules are the same as the normal IDF flow, you may refer to the Isolation Fence section for more details. Fence is needed only between IM Pblocks, irrespective of whether they are nested IM Pblocks or static IM Pblocks. A fence is not needed between the DFX Pblock and IM Pblock. A fence between the static IM Pblock and nested IM Pblock can be inside of the DFX Pblock or outside the DFX Pblock.
In the following figure, the DFX Pblock and the nested IM Pblock shares the same boundaries, and the fence between the nested IM Pblock and the static IM Pblock is outside of the DFX Pblock.
In the following figure, there is no gap between the DFX Pblock and the static IM Pblock, and the fence between the nested IM Pblock and the static Pblock is inside of the DFX Pblock.
Nested IM Pblocks inside of the DFX Pblock also need a fence and follows standard IDF fence rules. The fence between the nested IM Pblocks is always inside of the DFX Pblock. In the following figure, nested IM Pblock1 and nested IM Pblock2 has an 1PU fence inside of the DFX Pblock.
The following image is the complete example floorplan with two static IM Pblocks, and two nested IM Pblocks inside of a DFX Pblock.
Similarly, the fence between the nested IM Pblocks of two DFX Pblocks can be inside either of the DFX Pblock or outside of the two DFX Pblocks.