Minecraft wiki entry for Bastion_Remnant, associated text: Bastion remnants generate in all Nether biomes except basalt deltas, although a bastion may extend into one. If a bastion tries to generate in a basalt delta, the bastion will not generate, leaving the region empty. To generate the structure, the game splits the Nether into regions, in which either a nether fortress or a bastion remnant can generate. The regions are 432×432 blocks in Java Edition and 480×480 blocks in Bedrock Edition. Each region has a 4-chunk separation located on the south and east borders of the region in which neither a fortress nor a bastion can generate. This leaves only a 368×368 block section in Java Edition or 416×416 block section in Bedrock Edition where a structure can generate. Two structures will never generate in the same region, however they might overlap if they generate close to the separation border. In Java Edition, the chance of a bastion generating instead of a fortress is 3⁄5 (60%), while in Bedrock Edition the chance of a bastion generating instead of a fortress is 2⁄3 (66.6%).