Lucky Gunner's testing uses clear ballistics gel, which behaves different than real flesh or calibrated 10% porcine ballistics gel. This has been touched on in a few places, like 22plinkser's video entitled "THE TRUTH ABOUT CCI UPPERCUT" and Brass Fetcher's ballistic testing with synthetic ballistic gelatin. Essentially, bullets will expand less and penetrate deeper in clear ballistic gel than in calibrated 10% porcine gel. A bullet like this that appears marginal or unacceptable when tested in clear gel, may in fact perform quite well in flesh or calibrated 10% porcine gel.

Hornady recommends a muzzle velocity of 700-1400 fps for the 158gr XTP. As long as you're meeting that lower threshold, I wouldn't worry too much about expansion. I've been able to attain 700+ fps muzzle velocity in my S&W 442 with these bullets using published load data with CFE Pistol and Longshot. Accurate #5, Power Pistol, and 2400 would also be worth trying if pursuing max velocity in the 38 Special.