The taming effectiveness is used for more than just the bonus levels and is also affecting the multiplicative bonuses applied to certain stats. For example, a Rex have 100% base melee, an increase of 5% per wild point, an increase of 1.7% per tamed point, a 7% additive bonus and a 17.6% multiplicative bonus. If your tame only have 50% taming effectiveness, it will only receive 17.6 * 0.5 = 8.8% multiplicative bonus, etc. Which means that you can have multiple possibilities from different amount