When Gravity Readings Just don't make sense / Should I blend

TLDR: I have a beer fermenting that because of bad efficiency and some gravity black hole that happened during my boil, is overly bitter compared to the lower-than-expected gravity. Should I try brewing a small batch of maltier beer and blending it?

Longer version:
Brewed the following IPA-borderline-IIPA this past weekend. I have been brewing in a bag and typically getting around 75% efficiency. This time I did a superfine double crush through the mill, 75-minute mash (as usual for BIAB) with mash hops, and a single batch sparge in a spare fermenter with 170* water. The only difference is I didn’t do a 10minute mash out.

I am dumbfounded because after my ‘lauter’, I had 7.5 gallons of wort @ 1.047 pre-boil. Based on the 90 minute boil I was doing, I figured I would be down to at least 6 gallons as my blichmann burner evaporates like a mofo. So:

7.5 gallons @ 1.047 = 352 gravity points
6.0 gallons end volume = 1.058 OG PLUS 1# cane sugar, which should have added about 8-9 gravity points. 1.067-68, not the end of the world.

First off, my efficiency was miserable this time (total grist of 14.75# = 545 possible gravity points, 352/545 = 64% efficiency or ugh. Have NO IDEA why it was so bad.

Anyway, here is the weirdest part. I decanted the wort after chilling off the trub, aerated like crazy, and took a small refractometer sample. 15 brix, or about 1.060. WTF? Since this was bordering on a IIPA, and most of my hops were late, I went a little nuts with hop additions, bittering to 105.8 calcuated IBUs thinking that a BU:GU ratio of 1.38 was a touch high, but wouldn’t TASTE that bitter, as most were late. Then, when I had this abysmal gravity of 1.060, my BU:GU ratio became more like 1.76. Ouch. And bitter.

I gave this a taste tonight, and it was pretty damned bitter (not terrible but bitter, even for my tastes). It is super early (pitched 2 packs of US-05 Sunday 12/9 @ 10pm), as I was adding 3oz of dry hops per Tasty’s method of tail end of fermentation, so maybe its not done fermenting…

Any thoughts on what could have happened with my gravity? It makes no sense at all. Also, could I brew and ferment one gallon of malty, high-gravity beer and blend? I’m thinking it might be worth a try.

Flight of the Phoenix IIPA
14-C Imperial IPA

Size: 5.5 gal @ 68 °F
Efficiency: 75.0%
Attenuation: 81.6%
Calories: 251.62 kcal per 12.0 fl oz

Original Gravity: 1.076 (1.075 - 1.090)
Terminal Gravity: 1.014 (1.010 - 1.020)
Color: 12.33 (8.0 - 15.0)
Alcohol: 8.17% (7.5% - 10.0%)
Bitterness: 105.8 (60.0 - 120.0)

Ingredients:
0.5 ea Campden Tablet - added during boil
12.75 lb (81.0%) American 2-row - added during mash
.5 lb (3.2%) Crystal Malt 20°L - added during mash
.5 lb (3.2%) Crystal 40 - added during mash
1 lb (6.3%) Melanoidin Malt - added during mash
1 lb (6.3%) White Table Sugar (Sucrose) - added during boil
1 oz (8.3%) Caliente (17.8%) - added during mash
1 oz (8.3%) Columbus (15.0%) - added first wort
.75 oz (6.2%) Magnum (14.5%) - added during boil, boiled 60 m
.3 oz (2.5%) Amarillo® (8.5%) - added during boil, boiled 20 m
.3 oz (2.5%) Centennial (10.0%) - added during boil, boiled 20.0 m
.3 oz (2.5%) Caliente (17.8%) - added during boil, boiled 20.0 m
.3 oz (2.5%) Amarillo® (8.5%) - added during boil, boiled 15.0 m
.3 oz (2.5%) Centennial (10.0%) - added during boil, boiled 15.0 m
.3 oz (2.5%) Caliente (17.8%) - added during boil, boiled 15.0 m
.5 oz (4.1%) Centennial (10.0%) - added during boil, boiled 10.0 m
.5 oz (4.1%) Caliente (17.8%) - added during boil, boiled 10.0 m
.5 oz (4.1%) Centennial (10.0%) - added during boil, boiled 5.0 m
.5 oz (4.1%) Cascade (5.5%) - added during boil, boiled 5.0 m
.5 oz (4.1%) Caliente (17.8%) - added during boil, boiled 5.0 m
.5 oz (4.1%) Centennial (10.0%) - added during boil
.5 oz (4.1%) Cascade (5.5%) - added during boil
.5 oz (4.1%) Caliente (17.8%) - added during boil
.5 oz (4.1%) Amarillo® (8.5%) - added during boil
1 oz (8.3%) Cascade (5.5%) - added dry to secondary fermenter
.5 oz (4.1%) Centennial (10.0%) - added dry to secondary fermenter
.5 oz (4.1%) Caliente (17.8%) - added dry to secondary fermenter
1 oz (8.3%) Amarillo® (8.5%) - added dry to secondary fermenter

What was the mash pH? What about post-boil pH?

I actually haven’t taken pH in a long time. The strips never work and I don’t have a meter. Probably not the best practice, but I haven’t had problems in the last 10 or so batches where I haven’t adjusted pH.

It’s the first place I would look for sudden efficiency changes - you’re tap water pH could have risen and pushed the mash pH too high for proper conversion.

If you really don’t like how it tastes. then blending would be a good option. I’ve blended beers before with pretty good results