This isn't about getting more bang for your buck because you have higher end software. Drake is certainly more affordable than either ATX or ProSystem, and it generally does the calculation too, but this is a recognized problem for software in this specific situation. Abby Normal's post above perfectly describes what happens sometimes when applying the iterative calculation where he said it's "the catch-22 where deducting SEHI qualifies you for a PTC, but then the PTC lowers the SEHI so much that it disqualifies you for the PTC."