Overlap not working when I Tile Large Documents for Printing in Adobe Illustrator

[1960sgal]

I have tried this for 3 days without siccess. I followed atutorial and read multiple instuctions online I still get a missing piece to my overlap in Illustrator. Instead of repeating the image on the overlap it is reducing the image by that much. I need to use this technique daily - this is not behaving accoring to any direction that I have found so far, Can anyone here help me out? See my settings in screen capture below. I am trying to add .25" Should it be -.25? 

[meliax]

Does anyone have an answer for this? I am getting really weird results when I tile across pages with 0 overlap - the tiles just don't match up and seem to be randomly different sections of the poster.

[Brad @ Roaring Mouse]

Don't forget that your printer may have a non-printable margin on the page size you are printing to, so if you select Tile Full Pages and set an overlap of 0, then you will be missing the 1/8" of image or so at the edge of each sheet. Set your overlap for something larger... say .5".

OR Select Tile Imageable Areas which will give you no option for overlap, but will give you all the image you need