Not using external server if stratum drops below acceptable number

Hi,

I'm hoping that this is a silly question.

I've recently built a new NTP server environment, with 2 GNSS devices, and
using an external Stratum 1 service. Where the local appliances are
configured as the preferred sources,
(I'm aware that two is not the ideal, but hardware was bought before I was
given the project to implement).

With end users/clients connecting to three peered servers running as
Stratum 2.

My question is whether there is an option to stop using a particular source
if its stratum drops below an expected value. I suspect that the answer is
that it's not needed, but I just wanted to get some clarity for my
own understanding.

For reference, this is what running 'chronyc sources' looks like from one
of the servers: (I apologise for the formatting, server names have been
changed)

^+ Appliance1.>     1  10   377   257    -37us[  -37us] +/- 1310us
^* Appliance2.>     1  10   377   585    -16us[  -23us] +/- 1263us
=- Peer2       2   8   377   343  +8024ns[+8024ns] +/- 1856us
=- Peer3       2  10   377   888    +22us[  +22us] +/- 2444us
^- ntp0.external                   2   9   377   427  +1310us[+1310us] +/-
  14ms
^- ntp1.external                   1  10   377   251   -290us[ -290us] +/-
3734us
^- ntp2. external                     2  10   377   991   -294us[ -301us]
+/-   11ms
^- ntp3. external                     1  10   377   375    +23us[  +23us]
+/- 6145us
^- ntp4. external                     1  10   377   156  -1634us[-1634us]
+/- 9992us


Regards,
Simon