check_snmp is odd when defining ranges for warning and critical - monitoring Domino Availability Index using Icinga 2

I am using Icinga 2 to monitor an IBM Domino server.
I have an Icinga Service configured to use check_snmp, monitoring the server availability index.
Icinga with Domino Availability Index monitoring
And I have finally understood how to properly configure the service to issue warnings and criticals based on a numeric return value.
The Domino SNMP oid for the Server Availability Index is
It will return a value between 0 and 100.
100 means that the server is doing fine handling its work.
I want my Icinga Service to issue warnings when the index is below 80.
And i want the Service to issue Criticals when the index is below 60.

The command line to test this looks like this:

/usr/lib64/nagios/plugins/check_snmp -H -o -w 80: -c 60:

It will return something like this:

SNMP OK - 100 | iso.;0;0;

100 here means we're doing fine.

Let's look at those -w and -c parameters.

I was lucky to find a page explaining how to use these: check_snmp
As the author says it:

you have to be aware that the ranges you put are the ones which do not trigger the warning or critical. (Which is ass-backwards IMO.)

In my service configuration file, here is how i put in the parameters:

apply Service "Domino Server Availability index" {
    import "generic-service"
    check_command = "snmp"

    vars.snmp_oid = ""
    vars.snmp_warn = "80:"
    vars.snmp_crit = "60:"

    vars.backup_downtime = "03:00-05:00"

    command_endpoint = host.vars.remote_client
    assign where match("skanderborg2",

Here's output from the Icinga UI, showing the custom variables, read from the on-disk configuration:
Custom variables