Stout and mashing

[HOPCousin]

I put together a stout recipe with 5% Roasted barley and have found that my efficiency goes down every time I use roasted Barley. Wondering if I Mash for 60 minutes with all other grains and then add the Roasted Barley and mash for an additional 30 minutes would I make my OG without running into efficiency problems whic hI don't have with my other beers?
Here is the grain profile:

81% American Two-row Pale
5% Roasted Barley
4% Caramel/Crystal Malt -120L
4% Chocolate Malt
3% Flaked Oats
2% Smoked Malt
1% Black (Patent) Malt

 

[Reno_eNVy]

There must be something else going on. 5% roasted barley will do nothing to alter your efficiency, especially not enough to notice.

 

[HOPCousin]

The only time I run into efficiency problems is with roasted barley. happened with an american style porter where I had around 1-2% and lost efficiency. Happened in the Founder's stout clone I did. Never happens with any of the other 18 or so beers I've brewed. I know Roasted Barley can really effect efficiency and it seems to for me. So rather than add base malt to compensate as has been shared before I wondering if anyone has tried this approach?