Failure to Roam. MacPro stays on same AP

Question

I was doing some testing on another discussion question when I found that my MacBook Pro running 10.9.5 will remain attached to the same AP (access point) no matter how strong the signal or how it changes.
The information below was gathered while moving from the house to the barn (about 125ft) and back again.
The house has an Airport Extreme 802.11ac (tower) and the barn has an Airport Express 802.11n 1st generation
The network is configured for Roaming, meaning both APs are connected via ethernet cable to a switch and both have the same configuration including "Create a wireless network"
I used Wi-Fi Explorer to monitor the signal strength.  On the way to the barn I was on the 5GHz wireless.  The barn is configured only for b/g/n compatibility so uses the 2.4GHz wireless.  Once at the barn, I had to turn off the wireless on the MacPro and turn it back on again to connect to the Barn AP.
On the way back to the house, the MacBook remained on the Barn AP even though the House AP had a much stronger 2.4GHz signal.  I had to toggle the Mac's wireless again to get it to switch APs.
It is my understanding that when roaming it is not suppose to work this way.  Rather, the Mac should have determined that it had a better signal available and switched itself.  Is this an OS question or is it particular to my MacPro?
NOTE: I have also installed Wi-Fi Notifier will sometimes pop up and tell me that my data rate has changed even though I have not moved.
-------------- Everything below was previously posted on a different discussion but it shows the steps outlined above and shows the Mac fails to switch.
Using Airport Utility 6.3.2 I get the following options for my Airport Express 1st Generation.  There is a similar option for Airport Utility 5.6.1 under the "Radio Mode" pull-down.  Using Wi-Fi Explorer ($3 on the App Store) I see that only a 2.4GHz signal is available even when standing directly next to it (vs both a 2.4 GHz and 5GHz signal from my Airport Extreme 802.11ac)
Point being that the Airport Express(n) does not appear to provide both 2.4 and 5 at the same time.
This Airport Express (n) is configured for a "roaming" network, meaning it is connected via ethernet back to the cable modem which also has the Airport Extreme (ac) connected via ethernet.
As an aside, and since I walked all the way over to the barn to check this out, my MacPro appears to still be using the Airport Extreme for its connection even though Wi-Fi Explorer shows a much weaker signal.  I am in the barn now.  The Airport Express is the top line in the graph which when at the house, disappears on occasion although it is always accessible via Airport Utility.  (The Airport Express(n) is the third in the list)
I am using Airport Utility 6.3 which shows that the Airport Extreme (ac) is the AP my Mac is running through.
My MacPro is the third Mac Address in this list 70:56:...
Interesting too, now that I am in the Barn, both Airport Utility applications do NOT have access to the Airport Express (n) even though Wi-Fi Explorer continues to show a strong signal from that system.  (BTW, I also have 4 bars of wireless in the menu bar)  (FWIW: I also quit and restarted Airport Utility)  Based on further information below, it appears that my MacPro is NOT switching to a 2.4GHz network.
As an experiment, I turned off my wireless on the MacBook and turned it back on again.  Airport Utility now shows me connected to the Airport Express(n) in the barn.
Here is Wi-Fi Explorer as I return to the house (approximately 125ft)  Note the colors have been reallocated and don't match the previous screenshots.  The list has also changed.
At this point, my menubar on the MacPro usually shows 2 bars but often rises to 4.  However, it is clear my MacPro is still connected to the Airport Express in the barn because response is horrid and Airport Utility still shows that AP is servicing my MacPro.  (I cannot show that screen shot since it is a popup that disappears when I move the cursor.)
To switch back to the Airport Extreme (ac), I have to shut the wireless on my Mac off and turn it back on again.
I assume that I am connected to the 5GHz subnet since Airport Utility shows my data rate is 450Mps.
Something I had noticed until now, it also shows that my PHY is 802.11a/n.
This brings up several questions, which I should post somewhere else since my only purpose here was to suggest that an Airport Express (n) does NOT broadcast in both wireless ranges at the same time.

Answer 1

my only purpose here was to suggest that an Airport Express (n) does NOT broadcast in both wireless ranges at the same time.
That being the case, we have already answered your other post, which included the same statement.....by noting  that whether or not the Express will broadcast on both the 2.4 GHz and 5 GHz bands simultaneously depends entirely on which particular version of the Express that you are talking about. You never tell us.
The A1392 will. The A1264 won't.