I do accept that some aircraft might have a standby AI in a varied location, as the panel space and other considerations permit. Presuming that such placement is defined in the original approved configuration of the panel, there will have been an assessment of the design, and following that, an approval. If the designdid not follow the design standards, there will have been consideration of the affect, perhaps even an equivilent safety finding. That information is not generally available. Ideal? Perhaps not, but the best that was possible with the design. Sometimes things like how much depth behind the panel is available dictate where certain instruments end up.
If the AI was placed "somewhere" on the panel as a part of a retrofit, or modification, either it went through a similar evaluation and approval process, with a DER/DAR, or local equivilent, or perhaps it is just not approved!
Glass cockpits are certainly causing a need to rethink panels in general. I'm sure that by the time I retire from flying, round instruments will be as uncommon as tailwheels are now!
By the way, the first time I flew G1000 was in a Caravan. Neither of us had flown the G1000 before. I flew while the other pilot worked out how it worked. The only thing that neither of us could figure out was where the slip indicator was in the display. Only after some deliberate wild skids and slips to see what moved, did we work it out. A good idea ultimately, but a little too subtle!