How to increase the speed of a projectile?

Question

I am working on a project where I am launching a projectile and according to the following snippet:

 // launches the object towards the TargetObject with a given LaunchAngle
    void Launch()
    {
        // think of it as top-down view of vectors: 
        //   we don't care about the y-component(height) of the initial and target position.
        Vector3 projectileXZPos = new Vector3(transform.position.x, 0.0f, transform.position.z);
        Vector3 targetXZPos = new Vector3(TargetObjectTF.position.x, 0.0f, TargetObjectTF.position.z);

        // rotate the object to face the target
        transform.LookAt(targetXZPos);

        // shorthands for the formula
        float R = Vector3.Distance(projectileXZPos, targetXZPos);
        float G = Physics.gravity.y;
        float tanAlpha = Mathf.Tan(LaunchAngle * Mathf.Deg2Rad);
        float H = (TargetObjectTF.position.y + GetPlatformOffset()) - transform.position.y;

        // calculate the local space components of the velocity 
        // required to land the projectile on the target object 
        float Vz = Mathf.Sqrt(G * R * R / (2.0f * (H - R * tanAlpha)) );
        float Vy = tanAlpha * Vz;

        // create the velocity vector in local space and get it in global space
        Vector3 localVelocity = new Vector3(0f, Vy, Vz);
        Vector3 globalVelocity = transform.TransformDirection(localVelocity);

        // launch the object by setting its initial velocity and flipping its state
        rigid.velocity = globalVelocity;
        bTargetReady = false;
}

Everything seems to work perfectly except:

1- Whenever I increase the velocity it gets beyond the target.

2- Whenever I decrease the velocity it does not reach the target.

So how am I able to increase the speed and reach the exact target?