This might have an obvious answer after I get enough sleep, but in case not, I will ask.
The English language can be ambiguous. How does that affect character virtues and flaws?
Take for instance Magical Focus in "Rings".
Does this affect all Ring target spells? All circular items like earrings, finger rings, nose rings, arm rings, etc? The sound of a tolling bell?
Usually you'd specify what you refer to. You are still limited to a category, the mere fact that this one language some players play in is imprecise in its use doesn't extend the category (unless your group decides to rule otherwise).
My group has a player wit the minor magical focus in "sus". That is, the genus of swines, like canis is to dogs and wolves.
He doesn't get his focus when casting Frosty Breath on suspicious people.
As @Daelnoron said, the player has to define specifically what he means by Ring, then you adjudicate if it is worth a Major or Minor focus.
Unless you have house rules, spell parameters are not suitable focus. There is the minor hermetic virtue Ring/Circle magic in the Donatores section of HoH:Societas that gives some unique benefit for such type of spell.
Moreover, you need to clarify with your groupe if Minor focus: ring (defined as jewelry item) applies to enchanted ring or not - people on this forum have different views.
In one saga, we created a new virtue in house: Minor enchanting focus: ring (or sword, or armor,...), which specifically applies to said item, but only for the purpose of enchantment. We felt that the Confraternity of Roland would have designed such virtue, then we extrapolated from there.