hokiefyd 

If you're talking about a traditional 2-pulley cage, and you're talking about bending the cage from what we see as a straight line into a "bent line", then it would make a difference (because it would effectively shorten it).

If you imagine a straight cage that's 4" in length, then the distance between the pulley wheels is 4". The length of chain stored by that cage will be somewhat more than 4", because it wraps around the pulleys, but the C-t-C distance is 4". Now imagine you bent that cage back 90 degrees (if that were even possible) midway between the pulleys. So you'd measure "down" from the top pulley 2", and then straight "back" from there 2"...you'd have a right triangle, yes? A^2 + B^2 = C^2. Instead of a 4" C-t-C distance, it'd be sqrt(8), which is about 2.8". Actual length of chain stored would be somewhat more than that because, again, the chain is wrapping around the pulleys. But we're not changing pulley size, here...we're simply changing the distance between them.

This is the opposite of the original discussion (pulley size), and really does get back to cage length. If you keep the pulley sizes the same, then shortening the cage (or reducing the distance between the pulleys) will reduce wrap capacity.

Anything that increases the length of chain that a derailleur can store (longer cage, larger pulleys, or even adding more pulleys) also increases the length of chain the derailleur can give back to the drivetrain system, which is really what chain wrap capacity is all about, right? (And, of course, the inverse is true about reducing storage.) With big-big and a straight-through derailleur, it's not really "storing" anything in the sense that you could theoretically remove it and make a single speed and the bike would still work. But as you take links away that the drivetrain needs by shifting to lower gears, those links have to go somewhere...and they "get stored" in the derailleur cage. Of course, wrap isn't a literal measurement of the number of links in a cage, but this measurement is a good way to compare the relative storage capacity of two different derailleur designs. And the more links (or length or however you wish to measure it) the derailleur can "store" in its cage system, the increased ability it has to keep chain tension when going towards the small-small combination.