I'm glad you asked this question. It's a more complex question than you might realize so here comes the full explanation.
ML Sound Lab IR's are never placed using eyes as that is a very reckless, unreproducible and therefore lazy way to judge a mic position. Every speaker is different even of the same brand (f.ex. V30 vs V30) and therefore requires a slightly different approach even for speakers in the same cabinet. If I would say my mic position is "Cap Edge" then a lazy person would probably only see one or two options. Take the mic to the left or right side of the speaker. But a speaker is a 360 degree object meaning that I can take the mic up and down, left and right but also anywhere inbetween inside that 360 degree spiral and still have a "Cap Edge" position. I would say there are realistically about 12 noticeably different Cap Edge positions per speaker. Also "Cap Edge" may not be the best position for all these different angles. Sometimes it's better to take the mic closer to the center or further to the side. That adds way more options than just 12. Well I haven't even discussed mic angling or mic distance etc. There are literally unlimited different ways you can mic a speaker.
But I don't think that's my job. I think a collection with too many IR's will be hard to use. Even when I've pre-selected a handful of IR's people are still asking for my recommendations. That's why I created the Ace folder. That is all I use personally. I have an extremely tight and scientific approach to what makes a good IR and for single mics the #1 position (Ace position) is the scientifically best microphone position out of 40-80 IR's that I shot at the spot. Positions 2, 3 and 4 are also extremely good IR's since they're still the top 10% of all IR's I shot. I can honestly say that sometimes picking the Ace IR is very difficult and I might have 3 IR's that are all perfectly fitting to be an Ace IR and I just have to pick one. For this reason I think having those 3 extra IR positions is a good safety net. The Alloy folders might have first 10 positions as something I could've thrown into the Ace folder and that is definitely my special sauce. That's where people should go and look for their dream IR's.
So to answer your question: It might be completely random. Most of the IR's tend to be somewhere inbetween Cone and CapEdge positions. If I can get away with having a mic really close to the middle of the speaker I will go for it but it rarely happens.
