Hmm, now that I look over the recipe I see I didn't take into account the Belgian candi sugar contribution to final gravity. So, I'll edit the recipe above to reflect this. Does this vibe more with their suggestion?
Well to start with, 20 Plato = 1.083 SG; *5 gallons = 415 gravity units (83*5).
Belgian Candi sugar 0.47 lbs (1.5 oz/gal x 5 gallons) x 46 (extract potential 1.046) = 21.6 GU. So 415 - 21.6 = 393.4
Then using the grain bill:
2-row 0.8975 x 393.4 = 353 gravity units contribution
Caramel 0.09 x 393.4 = 35.4 GU
Chocolate 0.0125 x 393.4 = 4.9 GU
Then using, GU / extract potential per lb / efficiency = lbs needed:
2-row 353 / 45 (EP for DME) / 1 (100% efficiency w/ DME) = 7.84 lbs DME
Caramel 35.4 / 33 / 0.75 (based on 75% efficient mash) = 1.43 lbs
Chocolate 4.9 / 29 / 0.75 = 0.23 lbs
The problem that I run into with conversions, is that steeping grains doesn't really contribute fermentables. So it was always my understanding that you keep the specialty grains the same as the all-grain recipe and then calculate the amount of DME needed that will contribute the entire fermentable sugar. In that case, the recipe would look like this (with the specialty grains kept in proportion to original recipe, based on 14.5 lb total grain bill):
393.4 GU / 46 (EP per lb) / 1 (efficiency of DME) = 8.55 lbs light DME
Caramel = 1.3 lbs (14.5 lbs x 9%)
Chocolate = 0.18 lbs ~ 3 oz (14.5 x 1.25%)
The bottom line is that it is extremely hard to get an all-grain recipe exactly like an extract with steeped grains recipe. Also, the ingredient percentages aren't going to match up once you trade DME for 2-row grain (it isn't a 1:1 trade).
If anyone has other comments and suggestions, please share. I'm by all means no expert on this. Sorry for the mix-up...
PS. BrewStef, what were their extract recipe ingredient amounts?