How can I require the Ubiquity preview area to remain a consistent height?

I'm attempting to load an image into the preview block. The image that is loaded depends on the input text after the command (requires ajax response based on input and then dynamic pull of an image). Sometimes the ubiquity box shrinks and only will display the top few pixels of the image. This seems to occur when the AJAX response is slow. Other times, it seems to know how large the image is and the dialog expands accordingly.

My question is, can I force a specific height for the command window? I have given my image a height attribute, but that's not working 100% of the time.

Thanks!