FBA results show different compared to TBSS

Hi :
The differences between TBSS and FBA is mainly depend on my design matrix. Firstly, I use fsl-glm to build a design matrix for TBSS analysis and then apply it in fixelcfestats. In FSL, the group factor is divided into two columns. But for FBA, it is better to combine them into one column to avoid matrix rank deficiency.
The covariates such as the TIV(~1500mm3) usually much greater than the other factors (age:5). This also generate noise in the design matrix. I used z-score to reduce the matrix condition number from 500 to 2 and finally solve the problem. Thanks for the answer by rsmith.GLM
Now, I can get the expected results from TBSS and FBA.