Asking help to create a spell

Hello everyone this night i had an idea for a spell but im having quite some doubt about the realisation

Wall of Eternal Question

This wall isnt a physical type , In a large band of 10m and 3 m thick any human penetrating in this zone . Get a strong desire to ask himself deep question which require a focus, so they stop moving, acting and even looking around. this spell require a penetration

Obviously it is a Mentem spell

Now Creo Mentem say nothing about it ....

Base 3 form word in someone mind ----> questions
Base 4 Put a thought or emotion in another mind

So i guess Base 4 +1 complexity of the spell

Now about to quantify a zone

If we look the CrTe spell 25 p 153 Wall of protecting stone
Base 3+2voice+2sun+2 size
size allegate the 25 pace wide 4 pace high 1 pace thick
could it be adapted to a CrMe ?Im not sure

Beside if we put CrMe Base4 +1touch +1 conc ( a maintining the spell would solve any problem of it) + 2 groupe (10 peop) +1 size (for people ) +1 size for the zone +1 complexity
it makes the spell CrMe35

A bit heavy for a wall but none can see magic in a bunch of people thinking ?

Could this also be Rego Mentem to control the targets mental state (confused, introspective?) as base 4? Also consider that making the target ignore the world around it is more Rego than creo?

Mm why not

we keep the same Base ?

ReMe 35 ?

The part of the spell that isn't to the strict guidelines is the wall shape effect which sounds more like a magical field. I'm not sure if you mean the zone to be like a ward-style effect that persists?

exactly by wall i mean a Magical Field and yes

The field would require a special target I'd say equivalent to group so +3 magnitudes (one higher than group for being non-standard)

This does seem more Rego than Creo. Changing a person's mental state to introspection. OTOH, you could use Creo Mentem to create the emotion(?) of self-absorption. Or use Perdo Mentem to destroy any feelings of curiosity,

What about the spell Lost in the Memory(MuMe 35) from A&A, page 33? Or The Stultified Peasant(PeMe 30), same page?

Not a big fan of the proposed Target in the OP for a "standard" spell, as it seems to overlap one or more Virtue-granted spell parameters (It's a smaller version of Target : Road for the Neo-Mercurians, in some ways, maybe some other Virtues in others.)

so If we use the MuMe 35 Lost in memory
(base 15 +1 eye +3 Moon)

and rewrite as a field :

Base 15 +1touch +1conc +2 grp +1 size

MuMe 40 ?

I would strongly suggest looking at "The Shrouded Glen" from the corebook as an example, albeit one where the target is larger and the "implanted idea" is "[strike]These are not the droids[/strike] This is not the place you are looking for".

In general, creating "magical fields" that affect those entering them is not something that Hermetic magic does. In fact, it could be argued that it violates the limit of Arcane Connection (and thus is off-limits for most magical traditions) in that it allows a magus to affect targets that are unsensed at the time of casting. Hermetic magic sort of goes around this by having "container" targets like Room, Circle, Boundary, or Road, that affect a well-delimited space with its own independent identity (a Room, a Covenant, a forest, a drawn circle etc.) and everything within it. There are a few exceptions, like Threading the Ashen Path (or however the Perdo Herbam spell of deforestation in the corebook is called) but they are invariably legacy spells from previous editions.

This "legacy" issue has one more twist to it - whether stuff that enters the container after the spell is cast is affected. In general, all new spells published in the Ars Magica 5th edition line seem to assume this is not the case (and it's made explicit for T:Group); but some legacy spells like The Shrouded Glen that made it into the corebook from previous editions do.

So. If you really want to be a purist ... no magical field for you that a) affects a "generic" area without its own identity and b) affects people entering it after the spell is cast. Both a) and b) could probably be violated, and have been violated in published spells (though it's not clear if those spells are the result of experimentation, integration of exotic magics etc.) but as a Storyguide at the very minimum I'd require some effort to avoid a).

You can certainly do it with a magic item that senses folks in the area and automatically casts a Mentem effect on everyone who enters the area. This costs time and vis for each place you want to imbue with the effect, though. The way I would go at it if my troupe really wanted the effect in the game as a spell is something like this. Make the area on which the spell is cast a special item - say, a rug (or a mirror etc.). Then, imbue that object with unnatural properties (see the Terram or Aquam guidelines). I mean, if you can change water into an hallucinogenic potion, you can probably turn a rug into swirl of hypnotic patterns. These typically require an appropriate requisite (in your case Mentem) on top of the Form of the object, plus at least one or two magnitudes.