2 Multiply your bench angles
Most lifters limit their thinking to incline/decline/flat when it comes to benches on chest day. The same principle of diminishing returns can occur with the incline and decline benches, not just the flat one. But it doesn’t have to be that way.
Take a look at the adjustable bench and the adjustable decline bench. Both can be used with dumbbells (presses or flyes) or with Smith-machine training. While you probably have a preferred position for your benches, one you automatically adjust them to, note that there are a number of intermediate positions you could be using as well.
For example, you could set your incline to a low position, a moderate one, or very steep. Each of those adjustments slightly changes how the chest musculature is recruited, both in the contribution from the front delts and from the upper region of the pecs. Similarly, you can dial up slight variations in how declines are performed just by repositioning the bench.
To maximize the chest growth, don’t limit yourself to just the three bench angles. Achieve more complete muscular development by exploring the various angles in between.