Add a height restriction to program.

I found a program that I like and it works well for quarry sizes but I was wondering if there was any way to add a height restriction to it so that i could use it to carve out areas I've tried but I'm not all that great at lua.

Pastebin Code: http://pastebin.com/Acewyb2T

With height restriction you mean the Y value in game?
So let's say…
Not lower than layer 15…?

I don't really feel comfortable making changes to a program without asking the author first, but here it is anyway:
http://pastebin.com/713dBiEu

If I didn't screw up then this should mine an area of 20 by 30 and 16 blocks deep:

programName 20 30 16

I really don't have time to test this now, so let me know if something goes wrong.