Perceived velocity can increase based on release point, how far they are getting down the mound before release (ie closer to plate), or by when you can pick up the ball,,,but I'd think that's more perceived by hitter than if you are in the stands. I often go by the ear test. I noticed when the ball starts getting over 81-82, it starts to hisss, the old pffffssssssstttt. Of course the low seam baseballs are harder to get that to happen. As mentioned a high intent delivery can deceive you as well.