The bottom line is this,
The Type Of Drumhead, The Tuning, The Vibration Of The Hoops, The Shell Configuration, And The Type Of Hoop Controls The Sustain Of The Drum!!!
Plain and simple.
My ears do not lie.
All completely true Bob, but there's one element missing that's not very well acknowledged. The suspension of a drum becomes more critical the smaller you go in both diameter & volume. If you'd tried that same test with a pair of 10" or 12" toms, the result would be different. From our own testing, anything bigger than 14", especially of floor tom depth, there's next to no difference in
head sustain between suspended floor toms & ones with legs fitted directly to the shell.
There is the other issue too, & IMO, the more important one, & that's shell sustain. The longer the shell is resonating, the longer the drum is producing it's full fundamental tone. This is the dominant short sustain tone that cuts through the band mix. In a live situation especially, head sustain is all but lost. Shell sustain is the difference between a full sounding tom & a flat sounding tom. Put simply, the more mass that's bolted to the shell (with the exception of thick shelled drums), the less the shell resonates, & the flatter/more attack focussed the drum becomes, irrespective of the length of head sustain.
What most players perceive as sustain, is in fact head sustain. It's related to shell resonance sustain, but not linked to it in terms of performance. Head sustain is largely dictated by bearing edges, tuning, head selection, & hoops, & is only slightly affected by shell sustain, hence only a small difference in head sustain between a floor tom with legs & a floor tom in a suspension device. Again, thinner shells will show this up more than thicker shells.