I will talk only about the Intuos2 and older models because this is my experience (and I scrutinized them quite a lot).
In more recent models, ( I mean Intuos2 compared to Ultrapads ) there seems to be an extra "Sensitive area" on each edge -- but, (at least on intuoses2) -- it only really affects a
single axis. For example, when your pen is going "over the top" and moving in that area, the cursor will
continue to follow the pen sideways correctly. But in terms of vertical coordinates -- it is always stuck at a minimum coordinates (e.g. 0) (this is analyzing the USB packets, not just looking at the screen). So it "looks" like it is still sensing the pen in that area, but it is not practical at all as an active area. So make sure you compute the active area size correctly and such a case is not happening.
Note: They did this so the pen does not appear to get "stuck" on the border when pen is near the edge. A typical issue with older tablets.
My experience with Wacom specs is the following: They are hyper precise to the tenths of millimeters (or to the rounding that is expressed it is displayed). Just one time their number was completely off on the web site (but fine in the manual) -- this was obviously a typo. Also in some cases (I think this is not for Intuos 4) there is a menu strip at the top and this is a full active area but in the driver it is converted to a menu command and the active area is cropped. *If the driver supports* (not sure if this is the case) you could use that for drawing.
I am certainly not saying that Wacom is always right and you are wrong (wacom said many weird and bad things), but just that the active area does not fit with my experience (of the older models).
I keep a wiki with all the active area sizes -- if really this is different, I will update the wiki with a note.
http://wiki.bongofish.co.uk/doku.php?id=bongofish:tablets#intuos4_series Oh, I already have a note about this model -- sounds like this might be the typo I was talking about(?)
