  We study the origin of the soft X-ray excess seen in the 'simple' Narrow Line
Seyfert 1 galaxy PG1244+026 using all available spectral-timing information.
This object shows the standard switch between soft leading the hard band on
long timescales, to the opposite behaviour on short timescales. This is
interpreted as a combination of intrinsic fluctuations propagating down through
the accretion flow giving the soft lead, together with reflection of the hard
X-rays giving the soft lag. We build a full model of the spectral and time
variability including both propagation and reflection, and compare our model
with the observed power spectra, coherence, covariance, lag-frequency and
lag-energy spectra. We compare models based on a separate soft excess component
with those based on reflection dominated soft emission.
  Reflection dominated spectra have difficulty reproducing the soft lead at low
frequency since reflection will always lag. They also suffer from high
coherence and nearly identical hard and soft band power spectra in disagreement
with the observations. This is a direct result of the power law and reflection
components both contributing to the hard and soft energy bands, and the small
radii over which the relativistically smeared reflection is produced
transmitting too much high frequency power into the soft band.
  Conversely, we find the separate soft excess models (where the inner disc
radius is $>6R_g$) have difficulty reproducing the soft lag at high frequency,
as reflected flux does not contribute enough signal to overwhelm the soft lead.
However, reflection should also be accompanied by reprocessing and this should
add to the soft excess at low energies. This model can quantitatively reproduce
the switch from soft lead to soft lag seen in the data and reproduces well the
observed power spectra and other timing features which reflection dominated
models cannot.
