https://www.twitch.tv/which0neagain/clip/FantasticStrangeTitanHassanChop-H89Ff79tddxmrT2x

In this clip, we can see a player getting teleported up as their head briefly clips into where the next block is meant to be placed. If the player is halfway or more below the block and there is 2 blocks of air below the currently placing block, the player should be teleported down out of the way rather than up. Teleporting down is generally a safer bet when possible since explosions are restored bottom up.