Getting the “edge Y-values”

My problem is pretty simple, but yet I struggle to find an answer. Brief context, I have a sprite that moves accross the Y-axis according to microphone input. Beforehand, I prompted the user to record their lowest and highest note, calculated the frequency of these two notes and am using it as a reference for positioning the sprite on the Y-axis.

Let's say the lowest note is 100 Hz and the highest one 400 Hz. So if the player makes a tone of 100 Hz, the sprite should move down to the bottom of the Y-axis. To move back to the center (Y-position 0), the player would have to make a tone of 250 Hz (midpoint between 100 and 400).

So we know that for that player, 250 Hz equals to Y-position 0. But I need to know the Y-position equivalents of the lowest note (bottom edge) and highest note (top edge). When I move the sprite manually to the top edge and look at the Y-value in the inspector, it's apparently 4.58. But I'm not sure if hard-coding 4.58 would scale well across different screen-sized devices.
Screenshot here: https://i.ibb.co/pjrkSNV/Capture.png

I ideally want to have a method called FrequencyToY(float frequency) that converts a frequency value to the corresponding Y-value on the axis. I saved the lowest and highest frequency values in PlayerPrefs. Important note about the sprite movement, I don't want gravity. The bird should just smoothly move to the corresponding Y-position every time the player produces a tone, and stay in place otherwise.

This is my current script attached to the sprite:

 public class Player : MonoBehaviour
 {
     public AudioSource audioPlayer;
     public AudioMixer masterMixer;
     private float[] _spectrum;
     private float _fSample;
 
     //New code
     private float lerp_speed;
     private float lowest_y;
     private float highest_y;

     void Start()
     {
         //New code
         lerp_speed = 3;
         lowest_y = -4.58f;
         highest_y = 4.58f;

         //Code for microphone loop
         masterMixer.SetFloat("masterVolume", -80f);
         _spectrum = new float[AudioAnalyzer.QSamples];
         _fSample = AudioSettings.outputSampleRate;
         audioPlayer.clip = Microphone.Start("", true, 10, 44100);
         audioPlayer.loop = true;
         while(!(Microphone.GetPosition("") > 0)) { }
         audioPlayer.Play();
     }

     void Update()
     {
         //Calculate frequency of currently detected tones
         audioPlayer.GetSpectrumData(_spectrum, 0, FFTWindow.BlackmanHarris);
         float pitchVal = AudioAnalyzer.calculateFrequency(ref _spectrum, _fSample);
         if(pitchVal != 0)
         {
             if (pitchVal < PlayerPrefs.GetFloat("lowestFrequency"))
                 pitchVal = PlayerPrefs.GetFloat("lowestFrequency");
             else if (pitchVal > PlayerPrefs.GetFloat("highestFrequency"))
                 pitchVal = PlayerPrefs.GetFloat("highestFrequency");
 
             //New code
             Vector2 goal_position = new Vector2(0, FrequencyToY(pitchVal));
             transform.position = Vector2.Lerp(transform.position, goal_position, Time.deltaTime * lerp_speed);
         }
     }

     //New code
     public float FrequencyToY(float frequency)
     {
         float relative_frequency = Mathf.InverseLerp(PlayerPrefs.GetFloat("lowestFrequency"), PlayerPrefs.GetFloat("lowestFrequency"), frequency);
         return Mathf.Lerp(lowest_y, highest_y, relative_frequency);
     }
 }