Detect how close the iPhone is to the Mac using BLE?

Question

I'm trying to detect if the iPhone is placed close enough to the Mac using BLE signal strength. I am using the following code to detect if the iPhone is in range(and it works), but I don't know how to detect if the iPhone is 'close enough'. Like -30db for instance. Does anyone know how I can achieve that? Any comments/discussions are welcome :)

import SwiftUI
import AVFoundation
import IOBluetooth 
import CoreBluetooth
 import Foundation

  class BluetoothSearchDelegate : NSObject, IOBluetoothDeviceInquiryDelegate {
func deviceInquiryDeviceFound(_ sender: IOBluetoothDeviceInquiry, device: IOBluetoothDevice) {
    print("Found Device \(device.name ?? "nil")")
   }

func deviceInquiryStarted(_ sender: IOBluetoothDeviceInquiry) {
    print("started")
}

func deviceInquiryComplete(_ sender: IOBluetoothDeviceInquiry, error: IOReturn, aborted: Bool) {
    print("completed")
}
   }

 struct ContentView: View {
let delegate = BluetoothSearchDelegate()
let inquiry: IOBluetoothDeviceInquiry

init() {
    self.inquiry = IOBluetoothDeviceInquiry(delegate: delegate)
}

var body: some View {
    Button("Bluetooth") {
        inquiry.start()
    }
}
 }