So he had 10 Strength (Modifier) and it continued to show him rolling as high as 46 on defensive checks while testing. This means something is calculating more than once.Wiki wrote:A character with this feat can attempt a special knockdown attempt, which does not cause damage but does not provoke an attack of opportunity. A character may only knock down creatures that are one size larger than itself or less. The attacker makes a d20 roll modified by his strength bonus, and the difference between his creature size and the target creature size times 4. The defender makes a d20 roll modified by the better of his strength and dexterity bonus. If the attacker meets or beats the defender's roll, the defender is knocked down. Prone characters cannot attack. Characters receive a +4 bonus to attack prone opponents in melee, but a -4 penalty to attack them with a ranged weapon.
For reference I had improved Knockdown and was using charge feats, and was still rolling lower than him, though consistently in the 40s.