[忍]

Specifically detection spells...

What is the range of a detection prep? Is it Force x Force or Force x Potency?

The standard range of the sense a Detection spell grants is the spell’s Force x caster’s Magic in meters as a radius from the target of the spell.

When the spell is released from the preparation, it goes off as though it were cast by a magician. The Spellcasting Test uses the preparation’s Potency in place of Spellcasting, and the preparation’s Force in place of Magic (with the Force also serving as the limit).

Seeeeeeems straight forward, but then it wouldn't be 5e.

[Shinobi Killfist]

I've gone with forcexforce as it fit the RAW closer IMO.  But if I think about it it creates a weird situation where preparations can have a much larger range than what I'd expect is likely for spellcasting a least out of the gate. And thematically preparations are generally supposed to be at least a bit weaker.

[SunRunner]

Looks like Force X Potency to me.

[Beta]

I'm pretty sure that it is Force x Force [Force]. 

Which actually would make alchemical detection spells kind of decent if it was easier to get their dice pool up.  Let's say you'd managed a pretty good prep, at force 6 potency 3 (average result for throwing 15 dice in alchemy).  You would get a nice 36m radius, but rolling only 9 dice for the preparation means you are only averaging 3 hits, which makes a somewhat unreliable detection spell.  It certainly beats nothing, but for something you have invested in heavily enough to have 15 dice in, that is not overwhelming.