The vertical height gained from using a spear with Lunge is inconsistent based on the client's connection and framerate

On high fps, roughly 144 with vsync, vertical height gained from a spear with lunge is 1.5 blocks. When FPS is set to 10, I can get 2 blocks of height. My friend who is on a laggier PC with a bit of ping delay, can jump 2 blocks even with higher frames roughly 200, while I can not.