With HILIC mode, sample elution (retention) decreases as you increase the polarity of the organic solvent. Based on this information, good HILIC column wash solutions usually use alcohols in place of ACN (IPA, Ethanol and Methanol; with Methanol being a stronger eluter).
The use of additives, buffers and pH can all play a role in retention and separation plus improve reproducibility. When developing methods, be sure and evaluate their role. Because of the low water content of most methods, buffers must be chosen carefully to insure full solubility. Ammonium formate and acetate are popular as are acids such as formic acid. Regarding pH, the low aqueous portion will mean that the actual pH of the final solution will be much closer to neutral.