[lxgr]

I could imagine that in a head-on intercept of an Iridium satellite, some of the debris might make it into higher or lower orbital shell, but to be fair I don't know how realistic that actually is.

[jcims]

https://en.wikipedia.org/wiki/2009_satellite_collision

[lxgr]

Oh, I was aware of that even but not of that debris distribution graph. Thank you!

So it does seem like some debris making it into higher and lower orbital shells is quite likely.