Thread lead is 13/64 = .203125
1024 / .203125 = 5041.2307 pulse per inch at one to one ratio
But, at 20/32 ratio
5041.2307 / 20/32 = 8065.9689 p/inch
Question: are you sure about this lead? It wouldn't be a metric screw would it? 5mm = .19685 inch
BTW, if the controller reads the encoder as a quadrature encoder, you will know because the movements will be out by a factor of 4.