There is no magical ratio. Brooks's law applies, but it's detriment can be acceptable, if it's not impacting customer value. Don't focus on the input variables

There is no magical ratio. Brooks's law applies, but it's detriment can be acceptable, if it's not impacting customer value. Don't focus on the input variables (ie we have n engineers). Focus on the output variables. What are the SLA/Os for each service? If they're being met, then it's unlikely anything should change. Missed SLAs should trigger changes (see scaled agile framework).