Mode_compute = 6 automatically sets mh_jscale too small

Dear all,

When I use Dynare to apply Bayesian Estimation, mode_compute = 6 is chosen to avoid non-positive definite matrix problem. However, this routine seems to automatically fixes the mh_jscale = 0.00015 to obtain a target acceptance rate around 1/3. The small jscale makes the posterior very narrow around the mode, compared to the priors. It is however desirable to make the MC travel a vaster region. Anyone could help me with this headache?

It is really appreciated. Thanks.