Setting SRA on Rega?

Looking at the stylus of my dyna 20x2 with a magnifier lens today I discovered that the SRA was way off. I have 2 x 2 mm spacers under the rb700 and the arm is quite parallel to the platter if not tailed up! Is it normal that even in those theoretically fine conditions the SRA is not correct? Or is a defect of my cart? Should I put others shimmers to further raise the arm?
Was the SRA ok when the cartridge was first installed but has now changed? Have you just noticed that the SRA is off, but the VTA looks ok? Sometimes you have to make a bit of a compromise between the two.

A little more info would be helpful.
If I have to be honest I discover sra just recently. Before the only thing I knew was that the arm should be parallel to the record; so, two years ago when I fitted the cart I didn't check for sra. But from what I recall the stylus and the cantilever angle never changed through time. The cantilever though always seems to me to ride a bit too low, whit the tail of the cartridge almost touching the record. When I lower the stylus on the record the cantilever go a bit down, dunno if it's normal or if it should maintein his position.. any input from dv 20x2 owner would be very appreciated on this matter.
"The cantilever though always seems to me to ride a bit too low, whit the tail of the cartridge almost touching the record"

That IS way to low , raise the back of the tonearm more. Dynavector 20x2 has a very stiff cantilever so if the suspension is good the back of the cart should  not be riding so close to the record. A more forward rake will improve sound a lot!!

Matt M
Matt, when I say the back I mean tha part housing the cantilever. I don't know how to call it exactly but it's not really the tail. The arm is already lifted 4 mm with 2 spacers (yes with rega you can set vta). The arm is not even parallel but a bit higher on the back. I even remuved the mat to see if the srt would be better but it seems the 2mm would make much difference. I start to wonder if a fine tune of the sra really matter. Right now I'm more concern with the suspension of the cantilever.  It doesn't seem collapsed but respect at other pics I saw it seems to run lower. 
* would not, sorry
IMUO, SRA is over-hyped.