Muckle,
Your slicer is not breaking up the potato enough. The smaller the particle size, the better chance of complet conversion of starches. You are going to have to grind/slice the potatoes as much as possible. I use a commercial shredder with the smallest grate holes available. I wouldn't add very much water, perhaps enough to rinse your grinder. I recommend agitating the slurry while heating. I heat up to 210F and hold it for 90 minutes. Your 160 temp is not high enough to gelatanize the starches.
Upon cooling I add Termamyl SC, San Extra L and Viscoferm at their ideal temperatures and times making sure each has a least 25 minutes of working time. Do a starch test and be sure to add yeast nutrients and adjust pH for each enzyme you use. I also add more Termamyl at pitching time.