The 2 were almost identical in position from a far distance though. You had to look up close to see the difference.
To be fair, Sampras's normal toss is already halfway to one you'd have for a kicker.
To my knowledge, the feet stay in place, they only move vertically due to knee bend followed by jump before contact with the ball.
Just wanted to verify whether you used a platform stance, which you are. It's inherently more difficult to hide a serve were one somebody using a pinpoint stance. Such that if you were using a pinpoint serve, I would have said to not worry about that and just work on accuracy and placement. And so on.
First, the main thing you want to verify is whether your balance is correct through your toss and windup. At 3.5, it's rare to have that, unless they were involved with throwing sports. So, things to look for:
1) Do you feel your lower back straining or "compressed" in your windup?
2) Do you feel your weight shift to your back foot at any point in the toss or windup? How about when the ball is at its highest point?
3) Does your trunk open up before the racquet drop?
4) Do you feel like you self-consciously "create" a trophy pose? Do you lift the forearm into the trophy pose?
5) Do you "pause" at any part of your windup or takeback?
6) Do you feel like you have to self-consciously rotate your forearm for the racquet to hit the ball?
7) Do your hips move closer to the net?
8) When you land, does your front foot land into the court?
9) When you land, does your right foot kick up?
10) When you land, is your right foot almost square with the net and not pointing at the right side fence?
11) When you land, is your trunk bending to the left?
Generally, if you say "yes" to any of questions 1-6 or "no" to questions 7-11, there is probably a balance issue. You want to correct that first, because it's the foundation for your service mechanics. One of the side effects is that you become very dependent on the location of the toss in order to vary spin on your serves.