Shoot me if I am wrong.
But doesn't a false glidepath on an ILS appear on the earliest on 9 degrees on a 3 degreeglidepath? Being far off the localizer this could fool you to seem OK. But if you are established on the localizer this could be easily checked with among others OM crossing altitude or a decent rate of half of your ground speed. And if you are above, wouldn't it be safe to put in the localizer minima until you are established on the ILS glidepath?