I tried drawing some concentric circles in xfig and exporting as a
%Begin xfig output
%end xfig output
The issue lies with the picture environment, which is severely restricted. In particular, there is a limited set of circle sizes that can be drawn; see chapter 5 of the Not so short guide to LaTeX, or chapter 7 of Leslie Lamport's own book for more details. Indeed, in the log file, one finds the following:
LaTeX Warning: \oval, \circle, or \line size unavailable on input line 16.
LaTeX Warning: \oval, \circle, or \line size unavailable on input line 18.
LaTeX Warning: \oval, \circle, or \line size unavailable on input line 22.
Now, following @egreg's suggestion, one might try loading the pict2e package, but there is another complication. It seems that if one exceeds the maximum circle size in the original picture environment, then
xfig uses an
\oval command instead, so loading
pict2e won't help (though it can change the result). Looking at the xfig manual, it appears there is no support for
However, xfig can export graphics in many more modern formats, including
pdf. You can use these in your document instead; see chapter 4 of the Not so short guide to LaTeX for details. It is possible to use
pdf graphics in a picture environment and place other items on top of them (details here).