When using the "tp" command, you are being teleported to a Z coordinate that's bigger by 1 then the one you entered.

When using the "setblock" command, the block appears in a Z coordinate that's bigger by 2 then the one you entered.

*Description above happens when using coordinates without the numbers after the dot (example: using the Z coordinate 156 and not 156.51763...). When using a more exact coordinate, the "tp" command is teleporting you perfectly, and the "setblock" command spawns the block in a Z coordinate that's bigger by 1.