SWIG/BIAB (RIS & Sour Stout)

I'm not quite sure which specific sub-forum this should be placed since it pertains to about three. If it should be moved, please do so. Turned out to be a longer, more involved post than I had intended, sorry. So I'm going to attempt a SWIG (Split Wort of Increased Gravity,)/BIAB brew day on Christmas. The two styles I'm going after are a Russian Imperial Stout from the First Wort and a Sour Stout with the Second. Below is my recipe grain bill and calculations that I was hoping someone can review and let me know how far off I might be. At this point, I'm open to just about anything anyone tells me. RIS - 4.5 gallon batch (4 gallon to fermentor) Grain__________ Weight ____ SG ______ Points (Weight*SG) a. 2-Row_________ 14.5# ____ 37 ______ 536.5 b. Special B_________ .7# ____ 34 _______ 23.8 c. Wheat Malt_______ .5# ____ 37_______ 25.9 d. Aromatic Malt______ .5# ____ 35 ______ 17.5 e. Crystal 40L_______ .5# _____ 34 ______ 17 f. Roasted Barley_____ .5#_____ 29 ______ 14.5 g. Crystal 120L______ .2# _____ 33 ______ 6.6 h. Black Patient______ .2# _____ 27 ______ 5.4 i. Chocolate Malt_____ .2# _____ 34_______ 6.8 ----- Total Points: 654 Total Point / Gallons: 654/4.5= 145.33 (or 1.145 OG) Points * Efficiency: 145.33*.65= 94.46 (or 1.095 for 65%) 60/40 Batch: 2 * Points * Percentage= 2*145.33*.6= 174.396 (or 1.175) for 60% --- First Wort 2*145.33*.4= 116.264 (or 1.116) for 40% --- Second Wort A couple of things here....First, I'm not sure what the "2" is in the 60/40 batch calculations. Is that the number of wort runnings (in my example, 2, a first and a second?) That really doesn't make much sense to me since 3 runnings calculate out to larger OG when in reality, those numbers would decrease, right? Second, something seems off to me about this. When I run this recipe through hopville.com, my OG should be 1.094, which makes sense to me. However, the only number that comes close to that in the above calculations would be the Second Wort and that's still higher, which really doesn't make sense because 60% of the potential sugars would be gone. Now if I take my Points and calculate it (strictly) at 60/40%, I'm left with: 145.33*.6= 87.198 (or 1.08eight... damn emoticons) and 145.33*.4= 58.132 (or 1.05eight) ....Logically, that makes more sense to me. What am I missing?

I understand (would assume) the SWIG calculations are are probably pre-boil readings and I've calculated at 65% efficiency. However, even if I'm a little off in OG due to lower efficiency, it won't bother me much. I fell I can adjust if need be (adding DME to increase OG of either recipe or cutting back/diluting to decrease OG.)

Sour Stout portion: At the same time the main mash is going, I plan to mash some acidulated malt separately to convert it's sugars and when it's time, I'll combine the Second Wort with that acidulated malt mash. I was wanting to do a sour mash but can't get my head around how to pull it off [advised to keep the sour mash to ~20% of total mash (see step 5.)] I had wanted to collect Second Wort and combine Acidulated Malt mash, cool and hold at 95-122f, in it's entirety. Still not completely sure why this wouldn't work. Wouldn't the conversion have already taken place once the separate mashes were collected?

I think I'm starting to get why souring entire wort might be a problem. In a sour mash, the sparge takes place after inoculation and incubation. Meaning, conversion doesn't take place until after sour mash is complete. My idea has the conversion proceeding the sour mash, likely resulting in a pH level less than 5.2. I suppose the only way to try my ideas would be to sour mash the acidulated malt 2-4 days prior to brewing and combine with the Second Wort.