Yeah I always do put a flat plank across the tops of saw horses.
I started it decades ago and stuck to it all this time.
Its a little more like a workbench this way. Easier clamping by far, more secure sawing.
Also really good for sawing off short stuff laid along the length of a single horse.
A 1x4 makes all the difference, but a 1x6 is even better.
I usually end up inbetween width, using up some odd sized scrap or other. :)
Try it!
You'll see.
yours Scott