You can certainly do it equally, it just changes the thickness of the mash, which has some impact on fermentability. In your equation 3.41 Mash+3.41 Sparge = 6.82 boil, you haven't accounted for grain absorbtion.
Lets say that your making a bigger 5 gal batch, like 15lb grain bill. Your normal method would be to mash in with 4.7 gallon and sparge with 4.7 gallons. You get a total of 9.4 gallons, less +/- 2.4 gallons for grain absorbtion = 7 gallons boil volume.
You can still use your method with smaller grain bills, just adjust for absorbtion and increased fermentability (Due to a thinner mash).
What type of efficiency are you getting with this method? (seems like you would be under sparging on big grain bills and leaving lots of sugars behind)
Link to another mash/sparge calculator http://www.brew365.com/mash_sparge_water_calculator.php