Detect if falling with custom gravity

So I'm working on a state machine with a BUNCH of states and I'm trying to determine when the player enters the falling state. I see a bunch of examples that follow something like this: yVel = rigidbody.velocity.y; //y velocity of rigidbody

 if (yVel < 0)    //if it's negative, that means it's falling down so set to true
       isFalling = true;

That would likely work just fine IF i wasn't using a custom gravity script. The script applies a gravitational force to the rigidbody in the direction of gravity.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 [RequireComponent(typeof(Rigidbody))]
 public class GravityBody : MonoBehaviour
 {
     //override the monobehavior's rigidbody getter
     private new Rigidbody rigidbody;
 
     [SerializeField]
     private float m_Acceleration;
     [SerializeField]
     private Vector3 m_GravityDirection = new Vector3(0,1,0);
 
     public bool useGravity = true;
     public bool useFixedUpdate = true; //basically allows us to apply gravity in this script (true) or apply it in a class that uses it
     public float jumpForce = 10;
 
     /// <summary>The acceleration rate of gravity.</summary>
     public float Acceleration
     {
         get
         {
             return m_Acceleration;
         }
         set
         {
             m_Acceleration = Mathf.Min(value, 0);
         }
     }
 
     /// <summary>The direction of gravity.</summary>
     public Vector3 GravityDirection
     {
         get
         {
             return m_GravityDirection;
         }
         set
         {
             m_GravityDirection = value.normalized;
         }
     }
 
     ///<summary>Force applied to body</summary>
     public Vector3 Gravity
     {
         get
         {
             return -Acceleration * GravityDirection.normalized * rigidbody.mass;
         }
     }
 
     public RigidbodyConstraints Constraints
     {
         get
         {
             return rigidbody != null ? rigidbody.constraints : RigidbodyConstraints.None;
         }
         set
         {
             rigidbody.constraints = value;
         }
 
     }
 
     private void Start()
     {
         rigidbody = GetComponent<Rigidbody>();
         rigidbody.useGravity = false;
     }
 
     private void FixedUpdate()
     {
         if (useFixedUpdate)
             ApplyGravity();
 
         //For testing purposes only
         if (Input.GetButtonDown("Jump"))
             rigidbody.AddForce(GravityDirection * jumpForce, ForceMode.Impulse);
 
     }
 
     public void InitGravityBody(Rigidbody rb)
     {
         rigidbody = rb;
         useFixedUpdate = false;
     }
 
     public void ApplyGravity()
     {
         if (useGravity)
         {
             rigidbody.AddForce(Gravity);
         }
     }
 
 
     //Editor
     private void OnValidate()
     {
         m_Acceleration = Mathf.Max(m_Acceleration, 0f);
         m_GravityDirection = m_GravityDirection.normalized;
     }
 
 }
 

This means that won't work in this regards. How do I check if my player is falling in this regards? Is there a cheat I can do to do what I described earlier?