I have a question for anyone about this screenshot. I am newish to scrypt mining so this has been on my mind for a few weeks now.

I have R9 290 cards and R9 280x cards. The 280x cards never seem to have stale shares. I often get stale shares and job not found on my 290 cards. Why is that? Can I do anything to avoid this? Does it matter? If anyone could chime in that would be much appreciated.