ENH/BUG: update default threshold for _compute_rank

@agramfort @Eric89GXL @mluessi FYI
can't you just test that you have the good numerical values?

 264 = SSS task           5
 263 = SSS coord frame   4
 265 = SSS origin         3 floats
 266 = SSS in order       10
 267 = SSS out order     2
 268 = SSS nchan         306
 269 = SSS components     128 ints
 278 = Not explained     112
 243 = HPI g limit       0.98
 244 = HPI dist limit     0.005