Frist thing stop the Hen calling pronto! You don't want to train these birds or make them call shy.
It is fun to hear gobbles ~ we all do it but stop that. You know there are birds there.
Now the picture of the field
Look for an East facing edge because as the sun comes up it is the most likely spot for the birds to be at 1st light. Why? Sun warms it quicker and the birds are cold.
I'd spend some time just sitting and watching at various times. You have located some toms and surely both hens and toms will use that field. the more scouting at various times during the day and then seeing birds will help you determine the high traffic areas.
Finding tracks or a highly tracked area in the mud is a sure sign of good use.
Also if you can roost by just sitting in an area with no calling what so ever and listen for fly ups. I find a tree for me to sit against - sit back and watch nature go by. Fly-ups happen anywhere from 30 minutes to the last 5 minutes of daylight to dark. My rule of thumb - the last 10 minutes of daylight is best. Open field edges will be later and in dense woods slightly early and it is all due to the light levels.
Look for tall white pines at this time of the year. Usually a good roost tree. Broken branches, feathers, droppings, etc. If you find one try to figure out from where they fly up from and then fly down to - most times it is an small opening in the woods or a field edge. I have seen them drop straight down from the tree branch, but they need a flying angle start to get up there.

But most of all spend your time scouting. More walking and watching and very very little calling.
If you feel the need to shock gobble. Use a duck, crow, woodpecker, coyote howl, whistle, pressurized air horn. Even a slammed car door works at times. But I ask why? You know they are there. Now do your homework and try not to let them know you are there and you will kill one!

Hey Keep us posted - you will also get more responses I am sure......
Like you I use Google earth now as that tablet picture is worth a 1000 scouting trips.

Dave...JW

Ps - placing decoys out 40 yards is way too far. Stay between 10 and 20. You place them at 40 and the bird hangs up or stops at 60 then what. Place at 20 and the birds stops at 40 - well it might be in your range.
If you are sitting against a tree and are a right hand shooter place decoys to your left as you want the bird to concentrate on the decoy and walk past you.
If you use a blind you can place decoys at less than 20 easy.
No need to brush in blind go to the Reference section and read about it.

Pss
And lastly learn to use the natural shadows for any setup - keep the sun to your back if you can.