I did a bit of testing to understand where that 1mm or so of flex is coming from. If I apply force to the spindle to the point where the the spindle touches, I can measure that almost all of that movement is coming near the the rear foot. Of the three feet, that one has to absorb the most pressure from adding the weight of the platter. In my theory if the plinth were flexing or sagging in the middle, then the height at the feet would stay the same. However, since almost all of the height loss happens on the rear foot, it seems that the sorbethane vibration material in the rear foot is absorbing the added weight and compressing.
All 3 feet on the RP8 are adjustable, so I adjusted the rear foot to give me about 0.7mm of additional clearance. That seemed to get me back up to the exact level I had before adding the weight of the platter. I don't know if that is the right reference, but seemed to be a fair interim solution. Unfortunately, even though the RP8 feet are adjustable, the threading is very thin and loose. Also, the feet do not appear to have been designed to be used for leveling. If I adjusted all 3 feet, the whole table would have a bit of looseness and wobble, so the table really appears to be designed to rest fully on the feet.
On another note, I have seen Rega push their wall mount shelf for their high end tables, and this could be a factor in how their design evolved. That shelf is open with the deck only supporting the feet so that the spindle could never hit bottom. That is not a practical option for me, and a table of this quality should not have this problem.
I am definitely going to press my dealer for an official response from Rega. In the interim I have been able to fix the problem at least. I have a spare set of isolation disks from another product that I am no longer using, so I have inserted one of those under each foot. That has raised the table plenty so that the spindle doesn't touch. However, if the table is compressing by about 0.7mm in the rear, that seems like a lot on a table in this price range. I am not sure how that deviates from the reference design of the table for their "flat" setup, but I feel like Rega at least owes us some answers.
Thanks for your original posting on this as it helped me find a problem I didn't know I had...