Are your "much larger numbers" perhaps looking like a week plus a few days plus a few hours? For example, 60h turning into 1w 2d 4h? If so, that's just a function of how you've set your effort conversion factors and durations display preferences in the Project : Formatting inspector. OmniFocus doesn't want to display the duration in hours if you've given it permission to use days, and it by default thinks there are 8 working hours in a day, 5 working days in a week, so that 60 hour task is turned into 7.5 8 hour days, or 1 week, 2 days and 4 hours when displaying the duration, though if you look at the schedule, it's a 60 hour block.
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If that isn't the issue, come on back and we'll try again :-)