Falling starts is the best training methodology for this purpose. Hill sprints is another which trains acceleration phase, muscle strengthening of the quads and other neuromuscular factors of the body while the coach can see sprint mechanics in motion to make any tweeks accordingly.
Upright sprint positions during top speed is all technique and mobility. Stay on top of stretches, strengthen accordingly and your brain will find its sweet spot to display it's power. These cues lead to a lot of paralysis by analysis.