The agent boarding the flight should be more aware of those coming forward.
When I worked for FR at STN, there were 2 lines.....boarding cards 1-65 and 66-189. Anyone in the 1-65 group with a higher boarding card was sent to the back or made to stand and wait until the end. It's not fair on those with lower cards if you let everyone through regardless.
Surely EZY will have a limit on the amount of pax that can transfer into group A?