First off, why do you need to boost the cross sectional area of the VTR?

Are there any other fixtures besides the lavatory on this line?

Please explain the big change in direction more thoroughly.

I'm adding a bathroom to an old home. The existing vent area is less than the 4" drain. Hence I wish to use 2" vents for the new lavatory and new shower/tub. They will increase the total vtr area to slightly surpass the 4" drain area.

The lav drain has to drop through 2 45s to get around a beam, then a 90 to go horizontal, then into a 45, then a 2" wye to a 3" wye, then the 3" to 4" wye. That's a total of 225 degrees of bend before it reaches another drain line that has a cleanout.