@MisO69 welcome to burst!
you are submitting nonces, but they result in a deadline that exceeds the limit for the pool. info about deadlines and poc mining can be found at http://www.burst-team.us/index.php/about/
my suggestion would be consider switching pools to one that accepts higher deadlines (having something besides zero for your historical share for the block is better than, well zero). i believe pool.burstcoin.party is in the AIO wallet and has a high deadline limit. there is a spreadsheet of pools which will give some idea of their deadline limit provided at https://forums.burst-team.us/topic/1109/list-of-all-pools-overview
optimizing your plots won't increase your deadlines. it will decrease the hard drive read time and wear on the drive.
there is no benefit to mining a plot with multiple machines because it will still contain the same nonces. in order to benefit from mining with another machine plot more space on it with different nonces.
i hope this helps and good luck with the mining!