increase float when another one decreases

Hey im trying to create a float for example called spawnRate for my IEnumerator. The IEnumerator will under a while loop spawn objects. The function will keep spawning objects and before each spawn it will yield a waitforseconds and the float argument will be the spawnRate variable. There is a main object that moves around that will spawn these objects and i want make use of the rigidbody of this main object, its velocity magnitude float variable to control the spawnRate variable. Simply put, when the velocity magnitude of the main object decreases, i want the spawnRate variable to increase. The goal is for each spawn is a linear rate for when objects spawn so logically the rate should decrease once the velocity decreases.

 IEnumerator SpawnNet()
     {
         while(mainObj.GetComponent<Rigidbody2D>().velocity.magnitude > 1f)
         {
             //code//
             yield return new WaitForSeconds(spawnRate);
         }
     }

Im trying to create a float property for the spawnRate:

 private float _spawnRate;
     public float spawnRate
     {
         get
         {
             return _spawnRate;
         }
         set
         {
                     //alter the value based on: mainObj.GetComponent<Rigidbody2D>().velocity.magnitude//
             //code//
         }
 
     }

In the set i should write the code that alters the value of the spawnRate variable based on the velocity of the main objects rigidbody. But im not sure how to do it. As shown, i need to alter the value of the spawnRate based on the mainObjects rigidbody velocity. If you could help me it would be much appreciated

Thanks!