Suspension Confusion!

Hi all, I have a Defender 90 with a 5 inch total lift on her. This is comprised of +2 inch springs and 3 inch spring blocks front and rear. Now i know I need the longer 5" springs on the rear, but surely the front shock mount point has only been pushed down by 2 inches, surely hence I only need +2 shocks and standard turrets on the front? Just seems a bit pointless to spend more money on +4 shocks and +2 turrets?
Am i talking a load of bollocks or does my maths work?
Cheers