Problem with simulating a delay with velocity

I want to simulate a delay by repeating a sample with decreasing velocity. When i use equal steps it doesn't sound natural. When i do it by ear i come up with something like this: 127, 85, 65, 45, 33, 23, 12, 5, 3, 2. But it still doesn't sound smooth.
Does anyone know some kind of formula for this or maybe a better way to achieve a natural sounding delay?

I tend to go (only approx though)

127, 60, 40, 30, 20, 12, 8, 4, 2, 1

At the same time I'll start to add some Low pass at increasing levels which simulates the loss of high frequencies at lower velocities.

Thanks MPC Tutor, I'll try this.