I’m sorry my response took this long. Must have overlooked your question. Antenna lengths give better reception the closer to the wavelength the antennalength is. 1/2, 1/4, 1/8 and 1/16th lengths do work. 17.31 cm divided by half is 8.66 cm. 8.8 seems a bit long, about 1.6% too long. That might answer the shorter range. Could also be this is just a flunk antenna: it happens that antenna’s are just defective.
I would experiment with two pieces of 8.66 and 8.8 cm wires, see how the reception turns out. That rules out any defect in the stock 8.8 cm antenna.