I think spread of stance is fine, if you would just take a 3 second pause before going into your toss motion, concentrating on weight on the front foot. When the motion starts, what you do is fine.
A lower toss wouldn't hurt, since you currently wait for the ball to drop.
Part of the archer's bow is you lowering your hitting hand, so you hit upwards at about a 40 degree angle from the ground. If you can lower your elbow, that lowers your hittng shoulder, raising the toss shoulder.
A maybe experiement hitting flat serves with a conti grip slightly twisted towards backhand side, so you can better get the high hand, high elbow finish that most ATP pros use.