DPC detail for stone cills

[ruggers]

I'm about to have my cast stone stooled cills fitted into the face brick exterior wall and I need to know if it's best to use 100mm DPC underneath, or a larger stepped DPC.

 

What are the benefits if any of the stepped DPC as per my sketch?

 

My partial fill cavity wall is

100 face brick, 50mm air gap, 100mm PIR, 100mm block. The cills are 65mm in height x 175mm deep so that i can have them set back into the cavity by 25mm, which then allows the windows to do the same. Rear of stone cill to front outer face of PIR=25mm.

 

I planned to install a trimmed cavity closer under the cill, so a stepped angled DPC would interfere with this unless folded at 90 degrees.