The "Spell Storing" ability of the Shield Guardian says:
To do so, the wearer must cast the spell on the guardian. The spell has no effect but is stored within the guardian.
This seems to indicate you cannot cast, for instance, Fire Shield on the Guardian, because that has a range of Self.
This seems different than what is intended, as the wording for a ring of spell storing is:
This ring stores spells cast into it, holding them until the attuned wearer uses them....Any creature can cast a spell of 1st through 5th level into the ring by touching the ring as the spell is cast. The spell has no effect, other than to be stored in the ring.
The use of the word "into," which does not seem to indicate any range, versus the use of the word "on," which seems to mean the guardian is a target of the spell.
Which is the correct interpretation, grammatically, versus what is the RAI?