My terminology isn't quite correct, nor my math. I dug out my
"Complete Guide to Sharpening" by Leonard Lee. Here's what he has to
say about it:
"You can easily grind and hone a 15 degree bevel on the blade and then
put a 10 degree back bevel on the face of the blade (refers to his
diagram on P. 84). This would still leave you with a 25 degree
included angle, but you would now have reduced your cutting angle from
45 degrees to 35 degrees. You are still left with a 10 degree relief
angle, which is perfectly adequate for block-plane use. Possibly
more significant, you have sharpened the blade of your standard block
plane in a manner that will give you a lower cutting angle than
someone who sharpens a low-angle block plane in a standard fashion (12
degrees bed angle plus 25 degree bevel, a total of 37 degrees)."
I highly recommend this book.