I have been trying to figure out how to get the end gateways to spawn the player/entity that went through, on a specific block.

I have deleted all blocks in a 50*50 column centred on the gateway and it spawned a 19x19x6 platform of End Stone at about y8 in the NE quarter of what I assume is a 39x39 square centered on the gate. I spawned on the far corner. I thought this was my first breakthrough in determining what counts as a valid/invalid spawn location... so I deleted all but the corner block of the platform and pillared up leaving the valid spot unblocked to see if a higher y value would be chosen.

Nope, it spat me out on the edge of the main island. I got rid of the pillar leaving the block I had previously spawned on, the same block that the game generated in the void I created. Nope, it spat me back to the edge of the island.

I am losing my mind at an alarming rate. What are the damn requirements for the end gates?! Please someone, end my suffering!