I also found this - I have done this for my ‘source’ stacks - I even found a larger gap between the Fraim stacks (shown in pic above) was better in both adding a bit more separation and helping keep cables off floor.
When I had the 552 Pre it used to sit on the shelf below the ND555 (well it was CD555 then) - with mdium levels it all sounded great and the 552 did not need a top shelf in my system, just nothing below it and space above it and no PS in its fraim stack.
When the S1 Pre replaced the 552 Pre that generated an empty shelf - tried removing the shelf and having the Source on one level - it sounded bland and lost low-level detail - and it surprised me!
In the end I had to have the extra empty shelf so that the ND555(then CD555) source sat atop two Medium levels with Base level and mid shelf empty.
I then also found I needed one of the shelves to have a slightly different mass - previously I had determined that whenever I had two empty shelves in a single fraim stack they ‘talk’ to each other and couple resonances - you get something called ‘coupled oscillators’ effect which means each resonance feeds the other …it sounds awful.
Putting an object on the Fraim shelf solved that ‘rattle’ effect but creates others - in the end a larger custom slightly heavier Fraim glass totally solved the issue and sounded great so that is what I use for the Source fraim.
Why so much attention to detail - because it really made a huge difference in allowing the system to take-off and express music.
A lot of the changes I had to make were not what I wanted to make and went against what I wanted to do - but the system let me know clearly what worked and what did not and in the end made it easy to learn once I listened to the results and went along with what worked rather than what I had originally wanted.
Some attention to detail and personal experimentation with just position of expensive items you have purchased for your pleasure can be very rewarding.
DB.