I should have explained my decision, I apologise.
I chose to work from a base of 2 because level 2 usually allows one to "Learn one visible property of an object..." I decided an object's location would be such a visible property. I also noted that intellego herbam 2 permits one to "locate a plant" (and by extension plant based products, such as wooden doors). Extrapolating from that it seemed level 2 was a good place to start.
Indeed level 4 seemed to both be too much and not quite enough. I can hear myself saying "yes you can see the surroundings of your diamond pendant but it's dark so all you see is darkness..." and at the same time I wanted to focus on hearing as the primary sense provided by the spell. The fact that a spell based upon seeing from level 4 would become level 35 didn't exactly endear me to it.
I am aware of the limit of arcane connections but as one can use intellego to perceive behind a wall that one can see one should also be able to use it to perceive the location of the walls of a structure that one knows one is within.