Richard,
 
As promised, here are approximate continuum backgrounds for the full 
9-detector HESI array, for the equator, mid-latitude (i.e. the worst
non-SAA spots of a 28-degree orbit), and polar regions.  The 511 keV
line backgrounds in those three conditions are about 15, 25, and 75
counts/second (again for all 9 detectors summed).
 
I will eventually do a whole generation of better simulations using
GEANT and doing a much better job of background production by protons
in the spacecraft (there's an estimate in here, but it's the weakeset
part).  However, I don't think these will be done in time for the proposal.
In fact, I'm sure they won't.
 
These backgrounds are averaged over all possible relative orientations of
the Earth and spacecraft; however, if we are really in a polar sun-sync orbit,
there will only be one orientation: the Earth at 90 degrees to the spacecraft
axis.  I haven't simulated that, but I expect it won't change the polar
number by more than about 30% or so.              
 
Enjoy, and let me know if there's something else you need (I haven't seen
Said yet, so I haven't asked him about on-axis efficiency).
 
Continuum background postscript file follows.

-David
background rates, counts/sec/keV/(9 detectors)
5.0       10.       0.48         0.81         2.52
10.       15.       0.17         0.28         0.88
15.000000 20.000000 2.139235e+00 2.370794e+00 3.412814e+00
20.000000 25.000000 1.722155e+01 1.745613e+01 1.851173e+01
25.000000 30.000000 2.144295e+01 2.164659e+01 2.256296e+01
30.000000 35.000000 2.160508e+01 2.180384e+01 2.269826e+01
35.000000 40.000000 1.903861e+01 1.933669e+01 2.067807e+01
40.000000 45.000000 1.821894e+01 1.854890e+01 2.003369e+01
45.000000 50.000000 1.729378e+01 1.769078e+01 1.947728e+01
50.000000 55.000000 1.509177e+01 1.552087e+01 1.745182e+01
55.000000 60.000000 1.431246e+01 1.488047e+01 1.743652e+01
60.000000 65.000000 1.354256e+01 1.431677e+01 1.780070e+01
65.000000 70.000000 1.261279e+01 1.334572e+01 1.664390e+01
70.000000 75.000000 1.122798e+01 1.195923e+01 1.524984e+01
75.000000 80.000000 1.066737e+01 1.147327e+01 1.509982e+01
80.000000 85.000000 8.690546e+00 9.439667e+00 1.281071e+01
85.000000 90.000000 8.345228e+00 9.146948e+00 1.275469e+01
90.000000 95.000000 8.334127e+00 9.186757e+00 1.302359e+01
95.000000 100.000000 6.978275e+00 7.807509e+00 1.153906e+01
100.000000 150.000000 4.595064e+00 5.308472e+00 8.518805e+00
150.000000 200.000000 2.294044e+00 2.852743e+00 5.366890e+00
200.000000 250.000000 1.443798e+00 1.903767e+00 3.973625e+00
250.000000 300.000000 1.022404e+00 1.411327e+00 3.161481e+00
300.000000 350.000000 7.561303e-01 1.093470e+00 2.611498e+00
350.000000 400.000000 5.770344e-01 8.458357e-01 2.055442e+00
400.000000 450.000000 4.203407e-01 6.519792e-01 1.694353e+00
450.000000 500.000000 3.540010e-01 5.430313e-01 1.393667e+00
500.000000 509.500000 3.540010e-01 5.430313e-01 1.393667e+00
512.500000 550.000000 2.969279e-01 4.746793e-01 1.274560e+00
550.000000 600.000000 2.969279e-01 4.746793e-01 1.274560e+00
600.000000 650.000000 2.642175e-01 4.337379e-01 1.196580e+00
650.000000 700.000000 2.008893e-01 3.302104e-01 9.121555e-01
700.000000 750.000000 1.874836e-01 3.165436e-01 8.973136e-01
750.000000 800.000000 1.557053e-01 2.608374e-01 7.339319e-01
800.000000 850.000000 1.542068e-01 2.506663e-01 6.847341e-01
850.000000 900.000000 1.181657e-01 2.037297e-01 5.887676e-01
900.000000 950.000000 1.243010e-01 2.132784e-01 6.136767e-01
950.000000 1000.000000 1.026809e-01 1.758570e-01 5.051496e-01
1000.000000 1500.000000 7.188143e-02 1.293866e-01 3.881597e-01
1500.000000 2000.000000 4.103869e-02 7.386965e-02 2.216089e-01
2000.000000 2500.000000 2.851158e-02 5.132084e-02 1.539625e-01
2500.000000 3000.000000 2.250870e-02 4.051566e-02 1.215470e-01
3000.000000 3500.000000 1.742138e-02 3.135848e-02 9.407545e-02
3500.000000 4000.000000 1.447544e-02 2.605579e-02 7.816736e-02
4000.000000 4500.000000 1.341094e-02 2.413970e-02 7.241909e-02
4500.000000 5000.000000 1.072758e-02 1.930964e-02 5.792892e-02
5000.000000 5500.000000 1.029005e-02 1.852209e-02 5.556626e-02
5500.000000 6000.000000 9.312640e-03 1.676275e-02 5.028826e-02
6000.000000 6500.000000 8.653796e-03 1.557683e-02 4.673050e-02
6500.000000 7000.000000 7.889729e-03 1.420151e-02 4.260454e-02
7000.000000 7500.000000 6.714934e-03 1.208688e-02 3.626064e-02
7500.000000 8000.000000 6.273749e-03 1.129275e-02 3.387824e-02
8000.000000 8500.000000 6.603945e-03 1.188710e-02 3.566130e-02
8500.000000 9000.000000 6.479112e-03 1.166240e-02 3.498721e-02
9000.000000 9500.000000 5.215786e-03 9.388415e-03 2.816525e-02
9500.000000 10000.000000 4.686093e-03 8.434968e-03 2.530490e-02