I have noticed how on many of the weapons there will be attachments that don't look like they either fit on the rails and phase through them or will simply "float" above the rail. I do not know if this is a simple fix to stop phasing of attachments and rear iron sites but even then some of the attachments will conflict with some rear iron sites nonetheless. For the rear iron site conflict I would suggest moving the site elsewhere on the rail or removing entirely from said rail. The "floating" attachments simply need to be moved to proper location or attachment visually needs a size adjustment if the the attachment doesn't otherwise "fit" the rail. 
Thank you for your time.