Syntax for iperf3 to use over pair wireguard interfaces on a LAN?

[John]

I want to get iperf3 to benchmark a simple wireguard setup on my LAN.
I have two machines, foo is 192.168.1.228 and bar is 192.168.1.112.

These IP addresses are fully functional on their respective eth0
interfaces.  Each one also has a wg0 interface configured as shown
below.  I can get iperf3 to work over the non-wireguard interfaces,
but not over the wireguard interfaces.  What am using iperf3 wrong?
Did I misconfigure wg?

Details:
Here are the /etc/wireguard/wg0.conf files for both machines (I don't
care if the public/private keys are present/this is only a test
environment and it will allow others to simply copy/paste if they want
to test as well):

On foo:
####
[Interface]
Address = 10.0.9.15/24
SaveConfig = true
ListenPort = 500
PrivateKey = kLac+M+JJJ+gpsKo1DeUyfuwfDwGeKMj81+M3Z3mUkw=

[Peer]
PublicKey = y6DrsFVIgqBMc8joSuEytCpQEywk5dPKRoeLZZC9H34=
AllowedIPs = 10.0.9.16/32
####

On bar:
####
[Interface]
Address = 10.0.9.16/24
SaveConfig = true
ListenPort = 500
FwMark = 0xca6c
PrivateKey = 4EwMqSyvLaHrv5JvAAyKnmdbw9UN4rsjydkPXb5ll28=

[Peer]
PublicKey = SkBs9t96znOr+d60tgPlXkp7z6YABvfxD9KNVzZIP3I=
AllowedIPs = 0.0.0.0/0
Endpoint = 192.168.1.228:500
####

Again, both wireguard interfaces are up and connected.  For example, on foo:

# wg
interface: wg0
  public key: SkBs9t96znOr+d60tgPlXkp7z6YABvfxD9KNVzZIP3I=
  private key: (hidden)
  listening port: 500

peer: y6DrsFVIgqBMc8joSuEytCpQEywk5dPKRoeLZZC9H34=
  endpoint: 192.168.1.112:500
  allowed ips: 10.0.9.16/32
  latest handshake: 10 minutes, 41 seconds ago
  transfer: 32.45 KiB received, 8.24 KiB sent

If I run iperf3 in server mode on foo and in client mode on bar, it
works as expected using the non-wireguard interfaces:

On foo:
% iperf3 -s -B 192.168.1.228
-----------------------------------------------------------
Server listening on 5201
-----------------------------------------------------------
Accepted connection from 192.168.1.112, port 58575
[  5] local 192.168.1.228 port 5201 connected to 192.168.1.112 port 46261
[ ID] Interval           Transfer     Bitrate
[  5]   0.00-1.00   sec   107 MBytes   900 Mbits/sec
[  5]   1.00-2.00   sec   112 MBytes   939 Mbits/sec
[  5]   2.00-3.00   sec   112 MBytes   940 Mbits/sec
[  5]   3.00-4.00   sec   112 MBytes   938 Mbits/sec
[  5]   4.00-5.00   sec   112 MBytes   940 Mbits/sec
[  5]   4.00-5.00   sec   112 MBytes   940 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate
[  5]   0.00-5.00   sec   596 MBytes  1.00 Gbits/sec                  receiver
iperf3: the client has terminated

On bar:
% iperf3 -c 192.168.1.228 -B 192.168.1.112
Connecting to host 192.168.1.228, port 5201
[  5] local 192.168.1.112 port 46261 connected to 192.168.1.228 port 5201
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec   113 MBytes   950 Mbits/sec    0    281 KBytes
[  5]   1.00-2.00   sec   112 MBytes   939 Mbits/sec    0    296 KBytes
[  5]   2.00-3.00   sec   112 MBytes   938 Mbits/sec    0    296 KBytes
[  5]   3.00-4.00   sec   112 MBytes   938 Mbits/sec    0    296 KBytes
[  5]   4.00-5.00   sec   112 MBytes   944 Mbits/sec    0    308 KBytes
^C[  5]   5.00-5.33   sec  36.7 MBytes   939 Mbits/sec    0    308 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-5.33   sec   598 MBytes   942 Mbits/sec    0             sender
[  5]   0.00-5.33   sec  0.00 Bytes  0.00 bits/sec                  receiver
iperf3: interrupt - the client has terminated

When I try using the IP addresses of the respective wireguard
interfaces, I get nothing:

On foo:
% iperf3 -s -B 10.0.9.15
-----------------------------------------------------------
Server listening on 5201
-----------------------------------------------------------

On bar:
% iperf3 -c 10.0.9.15 -B 10.0.9.16
iperf3: error - unable to connect to server: Connection timed outa