The tapering Underfire is referring to is the reduction in the primary area OCH from FAF to minimums/MAPT. The OCH also reduces from 1000' to 500' from the IF to the FAF, and then reduces further from there.
Understood - but I certainly wouldn't refer to it as "tapering", as the primary surfaces involved do not slope...
Also, beware of comparing ILS check heights with non-precison heights. ILS heights
should take into account earth curvature, which can have more of an effect than you might think.