Gravfft - Parker expansion

Hello,
 
Quick query. When calculating the flexural "Moho" there does not seem to be a way of applying anything but the default first term in Parker's expansion, so anything beyond that (eg -E4) will generate a warning message as below and the program continues with E1:
 
c:\SS20-work>gravfft black1-topo.grd -Gblack1-topo_flex25km.grd -T25000/2670/3330/1030 -Z32000 -V -fg -E3 -Q 
gravfft: Warning: Due to a bug, or a method limitation (I didn't figure that yet) with the selected options, the number of terms in Parker expansion is reset to one
See examples in the manual if you want to compute with higher order expansion
*****
 
This error/warning is mentioned in the documentation, but I was wondering if there is a workaround if one needed to use higher terms of the Parker expansion in flexural studies, or is the first term sufficient? 
 
As with all these things, setting the mean Moho depth and a constant density contrast is a big oversimplification.
 
Is it feasible to compile a variable density grid for flexural studies?
 
Cheers
Lester
 		 	   		  
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