Are your index numbers for Mentor being "scaled" appropriately? Notice that its published indices scale them according to the "count-per-two-decks" TC method. Hence, the index for 15 vs. 10 is +15 TC. If you were to run the sim using the conventional "count-per-deck" TC, this play should kick in at +7 or +8 TC. Furthermore, if you're limiting the index plays that get tripped in by using a fixed TC number, even after making the appropriate TC adjustments, certain Mentor index plays will be will be deleted by mere virtue of its higher card tags.
There has to be something glaringly wrong with the Mentor sim results, and I'm not sure what it is. I can think of two cures.
The first would be to run Hi/Lo and Mentor, each playing all the hands according to strict Basic Strategy. Since both systems have a 97% BC, their yields should be virtually the same, as long as the larger bets are all tripped in at nearly the same advantage points.
The second would be to divide all the Mentor card tags in half, so that the deuces, 7's, 9's and Aces are all plus or minus a half point, while the 3's thru 6's and 10's are plus or minus one point (this does not change the accuracy of the system). Then -- run the two sims again, both using the "count-per-deck" TC method, and both systems using the exact same set of index numbers! Since Hi/Lo has a PE of 51% and Mentor's is 62%, I can't imagine Mentor not doing better (even though some of the indices should be slightly different due to the 7 and the 9).