Dear research gate members

I am new to UCSF chimera and trying to understand how to evaluate RMSD lb and ub scores.

From previous questions, it seems like if RMSD is over 2 then it is considered not valid, but what if the RMSD lb is lower than 2 (ex)1.221) and RMSD ub is higher than 2 (ex)3.28)?

It seems like people normally mention the RMSD ub number in their paper so I assume this data is not accurate/valid?

If so, do you have any suggestions on how to obtain lower RMSD values?

Thank you.