>...assuming a single setting (a single environment variable) is right
>for all the cronjobs.

try adding this:

FOO=1
* * * * * echo $FOO
FOO=2
* * * * * echo $FOO
FOO=3
* * * * * echo $FOO

to your crontab and see what you get.  environment variable settings
can be changed from job to job.

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