This note is continuation of https://drupal.star.bnl.gov/STAR/blog/fisyak/grid-leak-between-inner-and-outer-tpc-sectors-estimations-based-garfield.
To calculate  Ion Feed back (IFB) I use root macro ~fisyak/macros/tpcGL.C
There are two reason to do this calculations:

1. to make a baseline for comparison for different iTPC designs.
2. to estimate IFB from lower part on Inner (II) , upper part of Outer sectors (OO), and region between Inner and Outer sectors (IO). 

During these calculations the following parameters and assumptions have been used:

1. The wire geometry is the same as in N.Smirnov's calculations: https://drupal.star.bnl.gov/STAR/subsys/tpc/GridLeakSimulation.
2. Inner sector Anode wire potential : 1100 V.
3. Outer sector Anode wire potential: 1390 V.
4. The (closed) Gating Grid has (+/-) configuration (-115 +/- 75 V) i.e. the last  GG wire Inner Sector potential -40 V and the first GG wire Outer Sector potential -190 V.
5. Electrons are generate just behind closed GG (y = 0.1 cm, yGG  =  0), transported to anode wire, an avalanche is created, ions from the avalanche are transported.
6. The flux of ions (1/cm) is normalized to electron flux 1/cm.
7. IBF is ion flux just behind GG ( = -0.25 cm). 

Inner Outer region (IO)
 

Inner Inner region (II)

Outer Outer region (OO)

Conclusions

1. Ion Feed back flows per 1 electrons are quite comparable for all 3 regions: 
   1. IFB_IO = 7.7 +/- 0.3 
   2. IFB_II =  5.4 +/- 0.3
   3. IFB_OO =  8.4 +/- 0.3
2. The values of IFB (== GL) ~ 10 is quite close to Gene's Space Charge to Grid Leack ratio. 
3. The effect on distortion from "II" region (keeping in mind 1/R electron density dependence) is quite significant. Thus we (Gene) have to move from one sheet GL approximation to three sheets one.
4. It would be desirable to check that we do have  "+/-" GG configuration.  10 years ago it was intention to do (+-) configuration but nobody knows the real status of this. Wrong configuration (++ or --) will effect IFB_IO which can be used to normalization.