Distance, itad to signal?

You should place the ITAD so that the signal displays a red aspect at the same time the leading locomotive or car passes the signal and continuously displays red as the train passes, until after the last car or locomotive has passed and the timer on the signal returns it to a green aspect..  The purpose of the signal is to govern following movements by causing them to stop because the block ahead is occupied.

For technical reasons, you cannot place the ITAD right next to a signal bridge, so place it as close as possible to the signal bridge in the direction of train movement.  That way the signal will not display stop before the train passes the signal, but will assume that indication as soon as practicable after the train passes it.

If you run left-handed, then they are in the correct locations, although the one near the outside edge of the layout could be moved toward the signal for more realistic response.

And I can't tell from your photo, but the signal heads should face toward approaching movements.

Thanks.

Yes they are facing oncoming traffic. 

What about one for each direction?

When the two ITADs "disagree", one would light the proceed indicator and the other would light the stop indicator at the same time.  Obviously not what you want.  You can add a relay module to be the arbitrator.  About $10.  For example

Each ITAD would send its "stop" signal to the relay module for arbitration.  The relay module drives the stop indicator or proceed indicator...but never both at the same time.

I assume you're powering your ITADs with 14V AC Accessory voltage. 

14 volts yes  thanks again everyone