  Swift observed the SSS phase in RS Oph much fainter in 2021 than in 2006, and
we compare an XMM-Newton grating spectrum on day 55.6 in 2021 (2021d55.6) to
SSS Chandra and XMM-Newton grating spectra from days 2006d39.7, 2006d54, and
2006d66.9. We present a novel approach to down-scale the observed (brighter)
2006 SSS spectra to match the 2021d55.6 spectrum by parameter optimisation of:
(1) A constant factor, (2) a multi-ionisation photoelectric absorption model,
and (3) scaling with a ratio of two blackbody models with different effective
temperatures. This approach avoids defining a source model and is more
sensitive to incremental changes than modeling source plus absorption
simultaneously. The 2021d55.6 spectrum can be reproduced remarkably well by
multiplying the brighter 2006 spectra with an absorption model. Only for the
2006d66.9 spectrum, an additional temperature change is needed. We further find
the 2021d55.6 spectrum to resemble much more the 2006d39.7 spectrum in shape
and structure than the same-epoch 2006d54 spectrum with more absorption lines
with a deeper OI absorption edge, and higher blue shifts (1200km/s) than on day
2006d54 (700km/s). On days 2006d39.7, 2006d54 and 2021d55.6, brightness and
hardness variations are correlated indicating variations of the OI column
density. The 35s period was detected on day 2021d55.6 with lower significance
compared to 2006d54. We conclude absorption to be the principal reason for
observing lower soft X-ray emission in 2021 compared to 2006. We explain the
reduction in line blue shift, depth in OI edge, and number of absorption lines
from day 2006d39.7 to 2006d54 by deceleration and heating of the ejecta within
the stellar wind of the companion. Less such deceleration and heating in 2021
indicates viewing at different angles through an inhomogeneous stellar wind.
