Argh!(tm) I just love when I wrack for a few hours then
turn around and just see the solution like a big flashing
neon sign in the middle of the night!

Instead of:

  if ($interval % $counter == 0)
[download]

I should've used:

  if ($counter % $interval == 0)
[download]

No need to worry about "remainderlessness" that way.

Thanks all for input.
"dogs luv me cuz i'm crazy sniffable / i bet you never knew i got the ill peripherals"