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Hi Jack,
I would recommend thoroughly reading the downloaded document again. Just having a quick look at it just now revealed relevant content at least on page 10 ("Usually, the loading of greatest concern..."), 13 ("keep ground leads short"), 16-17, 29 ("Signal Source Impedance"), 29-30 ("Input Resistance and Capacitance"), 32, 33, 34, 35, 37 ("Bandwidth to the probe tip"), 40, 43.

The capacitance of *all* Hi-Z probes has a large influence at high frequencies, because the decreasing input impedance becomes an ever increasing short on the resistance. FET probes with their relatively small input capacitance present a higher high frequency impedance than most passive High-Z probes but their input resistance (as observed at DC and low frequencies) will still drown (be shorted) in the capacitive reactance at higher frequencies, just at a lower rate than higher-capacitive (passive) probes.
Low-Z (50 Ohm) probes have the advantage of a constant impedance from a relatively low frequency until their highest useful frequencies, albeit that that impedance is rather low.
Active (FET) probes isolate their output from their input, making a constant 50 Ohm output across their bandwidth impedance possible.

The bandwidth of probes is specified assuming a source impedance of 25 Ohm, see "Bandwidth to the Probe Tip" on page 47.

All this is a matter of physics, not a matter of choosing the right probe to completely get rid of the problem. You can only optimize by making the right choices. You cannot get 10 Mohm or even 1 Mohm input impedance at high frequencies with any regular (FET) probe. Also, transmission line effects (signal reflection, standing waves) would destroy the "improvement".

If you want to do measurements on high-frequency signals or signals with high-frequency content, always consider using Lo-Z probes like 1:1 50 Ohm, 1:10 500 Ohm or even 1:100 5 kOhm probes. These have relatively constant impedance and many can be made at home. Search for that on the Internet.

Among High-Z probes, FET probes with their relatively small input capacitance have the relative advantage of making the setup less sensitive to ground lead inductance, resulting in less "ringing". You can read about that in the ABC as well.

Raymond