1/4 overlap on a 6" tile will require an extra 1/4 of cutting space to the "right" of the tile -- this is in the positive direction for your X axis. The handibot is set up to home the tool so that when it is a 6" it is only about 0.075" from the hard stop. So you don't currently have that extra 1/4" that you need. It may be possible to get it by changing how your tool homes. If you open up "macro 3" in your macro editor (this is the little folder icon on your dashboard" at the top of the code you'll see some variables:
$x_backoff = .075
$y_backoff = .075
$z_backoff = .075
try changing your x_backoff to 0.275 -- if the tool can home and return the x to zero without bumping into the left side of the machine, you're in the clear. This will permanently change your home position, so if you have any jigs that rely on a consistent homing position, remember that everthing will be shifted to the left by 0.2" from now on.