Thank you Clayton for responding. Let me note also that I stand by what I am hearing. Yes, 30-40% is high, but I would temper that affect with another possibility which is room loading. It is possible that a small increase sounds huge IF for whatever reason, in my smallish room, the room sounds full and saturated, due to a tweak, to the point that my Hallowgraphs no longer function in the same way they did before the tweak, and for that explanation I am at a loss.
As I said, I had the grill cloths removed for one day before trying the screw tweak, and curiosity got the better of me, and I should have waited, although myself and others do hear differences (i.e. Dunlavys) when grill cloths are removed. I think I said there was a slight improvement without the grill cloths, (not 30-40%) and we also know that measurements as well are not always an accurate way of describing what one hears.
This is why I was suggesting that others try these tweaks, because if someone else hears ANY difference, something is going on. But this something needs to be verified, in this case by consensus.
For the record, the brass screws I used are slightly larger than the sheetrock screws so they do work, but changing back to the sheetrock screws could be a problem as those holes are slightly larger now, and would need a larger diameter screw IF the MDF is overused.
As far as the washer material, it is a Herbie's product, made for this type of application and I am assuming that it is different acoustically than the foam you are using. Now whether this has any influence on what I am hearing I have no clue without removing them and using my ears.
Tweaks are supposed to be a fun and interesting and sometimes rewarding way of hearing changes. Now, if these tweaks void a warranty or poise a danger to the integrity of the material then of course they shouldn't be done. Now unfortunately, I have no consensus in either direction, but based on what I am hearing, I am suggesting that you, Clayton, TRY some brass screws. After all, if this improves your product that's a good thing.