That's something I didn't handle in my patch, either. However, you could solve it like this:
(signal)
... [r $0-samples]
| |
[expr~ fmod($v1, $f2)]
|
[tabread4~ $0-file]
fmod() is a floating-point modulo, so it's like [wrap~] except it doesn't have to be constrained with 0-1.