You forget the abuse nexus for FairTax: the monthly "rebate" check. More compelling than reducing deductions is giving people more money outright - a more direct route to the people voting themselves money out of the treasury.
No, I don't forget it at all. It is clearly defined in the bill in a particular manner. I do not see it as an "abuse nexus", but as a one time thing necesary to keep the bill from being attacked as (or seen as) regressive.
Any increase to attempt to alter the prebate mechanism would affect all taxpayers adversely - they also happen to be voters. This makes any changes unlikely.