BIAB, extra base malt question

After watching the latest brewing TV episode on BIAB, I’m going to give an AG batch a brew using that method. I have both an 8 gal and my old 5 gal brewpots, so I actually plan on doing two separate mashes (each using half of the grain bill), then combining them pre-boil to come up with enough wort for a full five gallons of wort. My question relates to mash efficiency/adding some extra base grain.

On the episode, Jake Keeler mentions adding some additional base grain to the grist to compensate for the often poorer efficiency people get from BIAB. I’m going to start with my SNPA Clone (the one posted on this forum with help from the SN brewers) as I’ve drank a ton of SNPA through the years, and I’ve come up with decent results using the extract/spec grain conversion of the recipe so I’ll be able to gauge my results. I was wondering if anyone can recommend a general guideline for how much extra two row to add to the grain bill. Basically, would one pound be a decent starting point for a brew with 11.5 lbs 2-row and 1 lb C-60 per five gallon batch? More, Less? None at all? Any input is appreciated.

Cheers!!!

10% is a good starting point, so 1 lb should work.