I spent a little time on it yesterday. It is a little more complex than just the iframe sizes etc. The JS code for the calculator is exported from the same source that creates the flash version. It uses a framework called OpenLaszlo. In the exported code we seem to be getting the sizing issue. I did not write the original calculator, but I did have to get deep into it when creating the three sizes (normal, small and tiny).
To be honest it would require getting into the code and recompiling it. Knowing OpenLaszlo, I think that could be a bit of a time sink, and I certainly wouldn't recommend you going that route.
A better investment of time would be to get an all JS calculator and replace the original PoodLL calculator with that.
A quick google, came up with this:
If that works for you, or you find something you like better, let me know and I will try and put it in.