Cron job issue - twice as many emails sent

my Message limit for queue processing is set to 1000.

When I run the following cron:

www-data   php /var/www/html/bin/console mautic:emails:send --message-limit=1000 > /var/log/cron.pipe 2>&1

and check my spool - there are 2000 less in that directory.

When i increase the cron to:

www-data   php /var/www/html/bin/console mautic:emails:send --message-limit=3000 > /var/log/cron.pipe 2>&1

there are then 6000 less in the spool.

is there a way to make sure the number of emails sent is identical to what the cron job limit is?