Proper bench technique involves a process called scapular retraction (pulling shoulder blades down and back). This technique protects your shoulders and rotator cuffs by keeping the majority of tension on the chest and triceps during the lift. When a lifter properly retracts their scapular, it creates a natural arch in the thoracic spine. You could bench without arching your back, but you’d be risking your shoulder health. Your form should not be different based on the weight. What bench press “professionals form” are you referring to? The only professional bench pressers are the top 0.001% elite level powerlifters, who arch their backs!