Differences in appearance between FigureCanvasAgg and FigureCanvasWxAgg

FigureCanvasAgg seems to make fonts appear much larger that
FigureCanvasWxAgg. I am trying to get plots generated interactively
in a wx window to appear the same as those that I generate in a no
display batch script that outputs .png files. I use FigureCanvasWxAgg
for the former and FigureCanvasAgg for the latter. Is there a reason
why the same font size would appear much larger in FigureCanvasAgg
than FigureCanvasWxAgg. Is there another, better, way to achieve
uniformity accross png outputs and wx on screen display?

It doesn't look like one can use the FigureCanvasAgg for wx embedding
or the FigureCanvasWxAgg for png generation because the former will
not accept a parent window and the latter requires one.

If anyone has any ideas I would greatly appreciate suggestions.