@gdaddy1 First of all, those Wilson's are incapable of projecting 20 Hz into a closet. Frequency response specs are extremely misleading being taken at one meter. In short, they are not subwoofers which for the majority are poorly designed, cheaply manufactured and vibrate like crazy producing vast amounts of distortion. 

Having said all that there is absolutely nothing wrong with placing a speaker on top of a subwoofer as long as nothing rattles. Isolation feet are for the most part a joke. I would put some self adhesive felt feet under the speaker so that both surfaces are protected from abrasion. Make sure the subwoofer is dead horizontal or the speaker might walk off with the vibration.   

We can take the “height” issue off the table.  The Tontregers place the tweeter too low for my application.  The optimal height to raise the 40.3 is pretty close to the height of the sub. 

@soix 

vibrations negatively affect sound, so adding significantly more vibrations into the speaker is just never a good idea, period.

Agreed, but that's NOT what I'm suggesting. I want to eliminate all vibration going to the speaker and it's absolutely possible. I agree that the tweeter height must be within range of your ear height. If it's too low the speaker can be adjusted higher using stands. The only problem would be if they are too high. You are assuming this mismatched condition is "Likely" when it hasn't been measured and we don't know.

@mijostyn   

Isolation feet are for the most part a joke. 

Believe it or not there is big difference in the dampening affect from different materials used in vibration control. It's not a joke, it's science.

Don't Set Your Subwoofer In The Corner see here!

Mike

@lewl28  Too low can easily be raised higher by the simple use of some speaker stands. I cut mine to an exact height.

What crossover do you set you subs? 

A thought to ponder... when I move subwoofers around a room I could always, easily detect where the sound was coming from. I could always point at their location. The higher the crossover the easier it was to hear their location. If used in a stereo application this can affect the stereo image negatively. By placing the Harbeths in straight vertical alignment with the woofers will retain the stereo image and depth. They will still be adjustable. Initial placement YOU control, change the phase, change crossover level, change the volume, toe them in or out.. Plenty of adjustments. For me the center image was more important than attempting to find the last ounce of bass and separating the subs and have two speakers off the center image. 

Many others feel this way also.