Enclosure of well layer in fluid guard ring on chamfers

hi all，

I'm using IC6.1.8.500.15.I‘ve installed some fluid guard rings and created them.And they work perfectly on rectilinear edges.

One thing I found odd is that in some cases while on a chamfer,the well layer's enclosure is a little less than the number I was set in techfile,which causes DRC violation.

I never saw this in MPPs.

Am I missing something during the FGR installation or creation?

Other than add another well shape manually,is there a more elegant solution?

Also,after I install FGRs by the Install Guard Ring Form,there are a lot more parameters in techfile than I was filled in the form. 

I can understand yDiffEncCont and xDiffEnclCont ,these are minimum Diff enclosure W&L  I set in the form.

But where are parameters like diffEncCont1 diffEncCont2  metalEncCont1 metalEncCont2 come from , what the meaning of them?

Thank you.

Joshua