Forestay tension


Are there any guidelines for proper tension of the forestay?  Coming across the Indian Ocean, we noticed some lateral play that seemed more than previously noted.  The main mast rigging is tight and there's no 'rake'.  The movement of the forestay chainplate is well-within the rectangular bracket surrounding it below the turnbuckle.

If there's been a discussion, please send the message number; I found nothing with various search terms.
Drew and Lili
SM390, lying Durban Marina