The upper tier does have a maximum rake. (I think that is now 35° in the UK). However, upper tiers can have the minimum c-value of say c-60 (or less), because elevated and steeper tiers already offer better overall views with higher viewing angle/aspect and shorter viewing distance (if overlapping). So they can be brought forward slightly and/or their front rows lowered. As regards moving the lower tiers back. If you just stay in the same position and just lower the rake angle, the c-value reduces dramatically. C-value is far more noticeable and important in lower shallower tiers. However, the good thing is that it only requires a small movement of 1-3m (dependent on your initial starting point) to lower that tier's back row by several metres for the same c-value sightline. So while you lose that front row or 2, you might gain a multiple row overlap. It's a bit difficult to explain without a sightline modeller but when you manipulate the geometry you can generally create overlapping tiers in almost any given envelope. This then produces a greater capacity for footprint or conversely a smaller footprint for a given capacity. Hence the reason why GP accommodates nearly 40k on a similar footprint to Bolton's stadium, which only holds 28k.