open question about accuracy of measurement and frame of reference

goneasleep

this is pretty in line with the text book narratives explaining relativity..

if I'm on a train and I have a bouncing ball in front of me, and I have a single guess of its normalized vector in space at any point in time. I guess that it is moving down relative to me and if the ball doesn't lose any energy in its bounce and it stays perfectly aligned with my Y axis then I'm very close in my estimate 50% of the time. right?

now say I'm outside the train and I have the same chance to make a single guess of the ball's vector, I guess that its moving in a vector aligned with the train, now my guess is only exactly correct a small portion of the time ( when the ball reaches its max bounce, and when it hits the table) but I'm really close to it's perceived vector an increased % of the time. right?

and my guess gets even better the faster the train is moving, as its forward vector overwhelms the small up and down motion of the ball.

Am I wrong in thinking this way?

Thanks!