Outlined visually the positions of the chandra sources for 0931 and 1532, centered on the RASS source position, with the correct log(fx/fopt), and the offsets calculated from the RASS source.

It seems that in both cases the ROSAT source was probably not detected. The sources located closest to the expected RASS position are discussed below:

For 0931:
The RASS position is 142.829998,36.3730554
The WD position is 142.84526595, 36.36928494
RASS-WD offset: .7760754592'

The closest source to the RASS source position is located at 142.8057, 36.378942, at a distance of 1.2219', and a distance of 1.997426' from the WD. It has a u magnitude of 22.57+/-0.53, a g magnitude of 21.89+/-0.10, and thus a u-g value of .68, or with errors, between .25-1.11. It's log(f_x/f_opt)=.873428. Though it is the closest source detected, and perhaps at a plausible distance, it seems unlikely that it is in fact the ROSAT source because its chandra count rate of 5.8e-3, is much lower than the predicted chandra count rate of the RASS source, of 3.678e-2-1.559e-1.
The SDSS match to the chandra source, J093113.37+362244.0, objid: 587735240642789732, was offset from the chandra source position by 0.17028447"

For 1532,
The RASS position is 233.098415 47.446660
WD position is 233.10621952, 47.45025013
WD-RASS offset: 0.3829797676'

The closest source to the RASS position was at 233.1842, 47.401489, a distance of 4.412', and 4.3119980'away from the WD. It's u magnitude is 21.97+/-0.20, it's g magnitude was 21.03+/-0.03, and thus the u-g was .94, or somewhere in .77-1.11 when accounting for errors. The log(f_x/f_opt)=0.84207. It seems an unlikley RASS counterpart not only because of it's large distance, but also because its chandra count rate of 1.67e-2 was less than the predicted flux of the RASS source, 2.956e-2-1.092e-1.
Its optical counterpart, J153244.22+472405.2, objld: 587733442656731241, was offset from the chandra source by .17425710".