how to modify default gmdistribution parameters in evalcusters function?

I have use

optimum = evalclusters(Points,'gmdistribution','silhouette','klist',[1:10]); for calculating the optimum no. of clusters in which gmdistribution parameters with 'SharedCov' set to true and 'Replicates' set to 5.

1) I want to modify silhouette default distance value in this function form Euclidean to cosine. How can I do this?

2)

I got the following error with gmdistribution while calculating the no. of cluster. Help me to understand this and fix it.

Failed to converge in 100 iterations during replicate 4 for gmdistribution with 6

components

> In gmcluster (line 204)

In gmdistribution.fit (line 102)

In fitgmdist (line 135)

In clustering.evaluation.ClusterCriterion>@(X,NC)(cluster(fitgmdist(X,NC,'rep',5,'sharedcov',true),X)) (line 477)

In clustering.evaluation/ClusterCriterion/evalFun (line 309)

In clustering.evaluation/SilhouetteEvaluation/evalklist (line 94)

In clustering.evaluation.SilhouetteEvaluation (line 225)

In evalclusters (line 188)

In main (line 54)