I took five hearts of damage on a boat 18 blocks up.

I took five hearts of damage while stand in on a boat on a 3x3 platform 18 blocks up on a flat world with 200 tick speed. When I died it said I fell from a high place. The boat was here was on block 1.

 1  2  3

4   5  6

7   8  9

also the boat was half way off the platform