My rule is;Same tweeters
Same midranges
Same woofers
Same subwoofers
I wouldn't mix different tweeters, mids, woofers.
I woldn't make a woofer array of 7" drivers, then add a 12"
- just because - into the same box doing the same job. Either
bandpass both to do their own seperate job or make a full array of 7"
or a full array of 12".
Common sense rules.