C# float variable isnt behaving like its value

I have this set up so that my character has an energy bar that drains over time. I'm trying to set it so that if it's below 50% it drains faster, then same with below 30% and 20% with < 20% draining very quickly. about .008% per frame, I think. (the normal drain rate is about .0004% per frame) if I watch the energyDrainSpeed in the inspector while running my game, I can see it increasing but it doesn't behave the same as the number by itself does. what I mean is... if I change the DrainEnergy function so that there's just 500.0f instead of energyDrainSpeed, the character's energy drains a lot faster than it does when energyDrainSpeed is equal to 500.0f (or higher) I also tried setting the energyDrainSpeed to over 12000.0f but it definitely wasn't draining at a speed of 1% per frame. then when I replaced the variable with just 12000 in the script - like curEnergy - (12000 / 12000) - it did drain at a rate of 1% per frame.

Am I just getting lag or something?

this is the code I'm working on;

 using UnityEngine;
 using System.Collections;
 
 public class PlayerEnergy : MonoBehaviour  
 {  
     public float maxEnergy = 100;  
     public float curEnergy = 100;  
     public float energyDrainSpeed = 5.0f;
 
     public float energyBarLength;
 
     void Start()
     {
         energyBarLength = Screen.width / 5;
     }
 
     void Update()
         {
             DrainEnergy();
             AdjustCurrentEnergy(0);
     
             if (curEnergy < 50)
             {
                 energyDrainSpeed = energyDrainSpeed + 100.0f;
             }
             if (curEnergy < 30)
             {
                 energyDrainSpeed = energyDrainSpeed + 300.0f;
             }
             if (curEnergy < 20)
             {
                 energyDrainSpeed = energyDrainSpeed + 500.0f;
             }
         }

         void OnGUI()
         {
                  GUI.Box(new Rect(10, 35, energyBarLength, 20), curEnergy + "/" + maxEnergy);
         }  
     
            private void DrainEnergy()
         {
             curEnergy = Mathf.Clamp(curEnergy - (energyDrainSpeed / 12000) , 0.0f, maxEnergy);
         }  
         public void AdjustCurrentEnergy(int adj)
         {
             curEnergy += adj;
     
             if (curEnergy < 0)
                 curEnergy = 0;
     
             if (curEnergy > maxEnergy)
                 curEnergy = maxEnergy;
     
             if (maxEnergy < 1)
                 maxEnergy = 1;
     
             energyBarLength = (Screen.width / 5) * (curEnergy / (float)maxEnergy);
         }
     }
 }