Should the main feeders enter the panel at the top of the panel and not run across the branch circuits?
There is an available knockout at the top right corner of the panel. Home built in 2011
Doesn’t really matter. Welcome to the forum. 
I would have turned the panel 180, but as Robert said the arrangement is fine.
Pretty common installation…
Some where along the line I thought I learned that the branch conductors are not supposed to run across the SE cables. In this case the SE cables run on top of the branch circuits and are actually pinning them against the back of the panel leaving very little access to them for maintenance/repairs and creating a possible over crowded type of situation.
Seems to me that if the panel was turned over or the SE cables entered the panel at the top it would not even be questionable.
Thanks to all for the reply’s!!
I think you are mixing Service Conductors with Feeder Conductors. You are correct in that Service Conductors are not supposed to be in same raceway or enclosure as Feeders or Branch Circuits…except in locations where they both have to co exist…like Electrical Service Equipment.
In your example they are feeders and they are protected by an OCPD (Overcurrent Protective Device) so there is no harm. As for flipping an enclosure around 180 degrees…a very common practice as long as the enclosure is designed for that application.