I believe more weight (within reason) just makes your best glide speed higher so you come down faster, but wind up gliding the same distance (shorter time at higher speed). V speeds generally change by half the weight change percentage so being 10% lighter means going 5% slower (and parasitic drag is a function of the square of the velocity so only decreases by 2.5%), induced drag doesn't change because your angle of attack for best glide remains unchanged hence induced drag doesn't change.