dear all exciting team

I am calculating optical properties of cubic born nitride (BN) with considering electron-hole coupling effect.
Its parameters are: a=6.854 bohr, spacegroup=Fd3m, B is in (0, 0, 0) and N is in (0.25, 0.25, 0.25) and its experimental band gap is 6.4 eV (My GW-band calculation is in agreement with this). With GGA-PBE its band has been 4.45 eV. So, BSE input.xml is:

<input>
<title>BN zincblend</title>
<structure speciespath="/home/public/exciting/exciting/species">
<crystal scale="6.854039">
<basevect>0.0 0.5 0.5</basevect>
<basevect>0.5 0.0 0.5</basevect>
<basevect>0.5 0.5 0.0</basevect>
</crystal>
<species speciesfile="B.xml">
<atom coord="0.00 0.00 0.00" />
</species>
<species speciesfile="N.xml">
<atom coord="0.25 0.25 0.25" />
</species>
</structure>
<groundstate
ngridk="6 6 6"
xctype="GGAPerdew-Burke-Ernzerhof" gmaxvr="14" />

<xs xstype="BSE"
ngridq="6 6 6"
ngridk="6 6 6"
vkloff="0.01 0.05 0.03"
nempty="6"
lmaxapwwf="3"
gqmax="3.0"
scissor="0.071661"
broad="0.003674933"
tevout="true"
nosym="true">

<energywindow intv="0.0 1.0" points="1800" />

<screening screentype="full"
nempty="150" />

<BSE bsetype="singlet"
nstlbsemat="1 4 1 6"
nstlbse="1 4 1 6"
aresbse="false" />
<qpointset>
<qpoint>0.0 0.0 0.0</qpoint>
</qpointset>
</xs>
</input>

It run it without any problem, but in the "EXCITON_NAR_BSEsinglet_SCRfull_OC11.OUT" band gap is :

E_gap : 10.59033978 eV

Why it has large difference with the experimental gap?!
( also, in an another calculation, I used EFERMI.OUT and STATE.OUT of GW-calculation, but the gap became 10.59033)
(also, in an another calculation, I set scissor to zero, but gap became 8.7 eV and no 6.4). With a larger K-mesh, the results did not change.

Please help me. What should I do?

Best Wishes
Hajar Nejati