Reproducing the observed lcıs:
1223 illustrates the degeneracy
Epic-PN lc of RXJ 1223, rev. 561 (Jan 2003).
(0.12-0.5 keV). Haberl et al, 2003
Fit 1:

B0quad = 0.07 Bdip    s = 0.02 
B1quad = -0.08 Bdip   s = 0.02
B2quad = 0.53 Bdip    s = 0.03
B3quad = 0.45 Bdip    s = 0.02
B4quad = 0.52 Bdip    s = 0.02

c = 98.2    s = 1.2
x= 0.1        s = 0.2

c2= 0.02
Fit 2:

B0quad = -1.27 Bdip    s = 0.31 
B1quad =   0.95 Bdip   s = 0.12
B2quad =  1.00 Bdip    s = 0.12
B3quad =  0.43 Bdip    s = 0.12
B4quad = -0.11 Bdip    s = 0.12

c = 58.6       s = 4.5
x = 80.9        s = 3.3

c2= 0.007