cross-ref cumin to direct-ssh setup and expand on effects of using batch

Using cumin's batch size is still a possibility to avoid issues, but it
is preferred to configure yourself for direct ssh connections and avoid
using the batch size if not necessary.

if direct-ssh connection is not possible, then using the batch size hack
is still possible. using it does have some side-effects that one should
be aware of though.

small correction in the text after my tests today: the limitation is
imposed by the MaxStartups setting, not MaxSessions.

howto/cumin.md

@@ -165,16 +165,32 @@ change the path to cumin in the bash function.
 
 ## Avoiding spurious connection errors by limiting batch size
 
-If your ssh configuration makes all hosts use the same `ProxyJump`, you might be
-seeing some strange and fluctuating percentage of hosts will error out on
-connection. This is because you are hitting your ssh proxy's max connections per
-IP. This could be caused by the server's `MaxSessions` which defaults to 10.
-
-In order to avoid weird issues, you should limit your batch size to 10 or lower,
-e.g.:
+If you use cumin to run ad-hoc commands on many hosts at once, you'll most
+probably want to look into setting yourself up for [direct
+connection](doc/ssh-jump-host#when-not-to-use-the-jump-host) to the hosts,
+instead of passing through a jump host.
+
+Without the above-mentioned setup, you'll quickly hit a problem where hosts give
+you seemingly random ssh connection errors for a variable percentage of the host
+list. This is because you are hitting ssh server limitations imposed on you on
+the jump host. The ssh server uses the default value for its `MaxStartups`
+option, which means once you have 10 simultaneous open connections you'll start
+seeing connections dropped with a 30% chance.
+
+Again, it's recommended in this case to set yourself up for direct ssh
+connection to all of the hosts. But if you are not in a position where this is
+possible and you still need to go through the jump host, you can avoid weird
+issues by limiting your batch size to 10 or lower, e.g.:
 
     cumin -b 10 'F:os.distro.codename=bookworm' 'apt update'
 
+Note however that doing this will have the following effects:
+
+* execution of the command on all hosts will be much slower
+* if some hosts see command failures, cumin will stop processing your requested
+  commands after reaching the batch size. so your command will possibly only run
+  on 10 of all of the hosts.
+
 ## Example commands
 
 This will run the `uptime` command on all hosts: