An apparatus having a circuit and a decoder is disclosed. The circuit is configured to adjust an initial one of a plurality of reference voltages in a read channel of a memory by shifting the initial reference voltage an amount toward a center of a window and read a codeword from the memory a number of times. The window bounds a sweep of the reference voltages. Each retry of the reads uses a respective reference voltage from a pattern of the reference voltages. The pattern is symmetrically spaced about the initial reference voltage. The pattern fits in the window. The decoder is configured to generate read data by performing an iterative decoding procedure on the codeword based on the reads.