Yes, it's a bit confusing in the rulebook.
There is no rule anywhere (that I'm aware of) that places a hard limit on what the Force of a spell, spirit, or magic item is. When a Mage absolutely HAS to kill every mutha***ka in the room, Force 8-10 Stunballs are pretty common in fact.
Spells are fairly straightforward. You can cast spells at Force of up to double your Magic. Drain is physical of course once you go over your Magic when casting or summoning anything.
There's nothing stopping you at Magic 6 from attempting to Summon a Force 12 Spirit. With Initiation increases to your Magic attribute, you can go even higher. Same thing goes for Wards and Foci.
Foci above 6 are going to be pretty effing rare though and crazy expensive. In my games even powerful NPCs rarely have a Focus of Force 4.
Wards are probably the most common thing you'll find above Force 6. This is because groups of Mages can easily combine their Magic to make Wards equal to the sum of their Magic attributes. So if you're a rich corp with a bunch of Mages working for you, or a Magical society, you probably have quite a few Mages on the payroll and can easily pump out Force 10 Wards that will last for weeks before needing to be re-done, or if you're really rich, you can pay the Mages to make it permanent.
Your solitary Mage is a bit more limited though. You can over-cast a Ward to twice your Magic, but this means for an un-Initiated Mage a Force 10 Ward is a strain.
As far as Spirits go, generally unbound Spirits are going to be equal to the Magic attribute of its caster or less. Rarely is it worth over-casting and risking injury on a temporary Spirit. So generally Spirits above Force 6 are going to be bound spirits that Mages have taken special care to Summon and Bind. Sometimes these spirits will be summoned with Rituals. At least, that's how I use Spirits in my games. Bound spirits are also EXPENSIVE though, so your average Street Shaman isn't likely to have a Bound Force 10 Fire Spirit on standby.
