My P3 did the same thing. I always made sure the platter was level. I did this because that is what the record and arm wil be sitting on.
It's possible that the well in which the platter shaft and bearing are located is not perfectly vertical, which would make the cause the platter surface to be out of parallel with the plinth. In the situation you describe, it's more important that the platter surface be level than the plinth, since the tonearm and cartridge need to be level for the stylus to track with equal pressure on both sides of the record's grooves. However, if there is much misalignment between the plinth and the platter, I recommend that you take the turntable to a dealer that has experience with turntable setup and ask for an adjustment.
Okay - the more I'm thinking about this, the less this is making sense. Adjusting the pitch of the platter by changing the base that it's sitting on isn't going to do anything.
The ONLY element I have control over here is plinth. No matter how I adjust it, the relationship between the tonearm and the platter is going to remain the same because they are both mounted to the plinth. Adjusting the plinth out of level so the platter is level isn't going to change that.
The degree of error here isnt much and it's not in the plane that the tonearm moves across the record in - it's parallell to the tonearm tube. In other words, it's not like the needle is tracking "uphill" or "downhill" - hope that makes sense!
The more I think about it, the only thing this could potentially slightly affect would be VTA and even that would be negligible here especially since I'm using the Rega Exact cartridge.
This is all very interesting, especially since there's another Rega owner with the same issue. I'm beginning to wonder if it's another one of Rega's unusual design elements; although I can't imagine why they would do this. If anyone else has a Rega table and is willing to check - I'd be curious to see if they're all like this!
I have a Rega Planar 3 and a VPI Aries. With both tables, the plinth sits on a slightly different plane than the platter.
The only thing you should be concerned with is making sure the platter is level, as it is crucial that the stylus encounters a level surface. Put a good level on the platter with the mat removed. For the Rega, I used Post-Its, which are perfect for allowing you to get the platter level. Once I have the table leveled, I pull the Post-Its and blacken them out with a magic marker so they do not stand out. With the Aries, the feet adjust for leveling.
Hope this helps.
Don't worry so much about the tonearm/platter angle. What is important is the angle of the stylus to the record. That is why we have all of these adjustments, VTA, azimuth, overhang, etc. Get the platter level then adjust whatever you need to in order to get the stylus angle correct in relation to the now level record groove.
The RB-700 is a bearing arm, which requires a leveled pinch (actually the arm board). Otherwise, the arm will put more pressure towards the lower side.
On the other hand, a unipivoted arm (i.e. VPI JMW) is self-leveled which requires a leveled platter to maintain correct angular relationship with the record.
Sidssp - this is the most logical response I've gotten yet. So I should just get the plinth (and hence the armboard since it's bolted directly to the plinth) level and not worry about it. It's pretty much sitting at a happy medium between the two now after I adjusted a few things.
Dr_balance & Dan_ed - the problem with these Rega arms is that there are NO adjustments. Don't get me wrong, the RB-700 is one of the finest arms I've ever experienced but you can not adjust a single thing other than tracking weight and anti-skate.