Is it correct to assume that the drain/source area and perimeter of a two (or more) devices connected, as shown in the attached figure, are associated to only one of those devices? Below are some examples of the extracted devices from the figure. Extracted Spice without Flattening:

X0 a_63_n45# a_15_67# a_n33_n45# w_n263_n255# sky130_fd_pr__nfet_01v8 ad=1.395e+11p pd=1.52e+06u as=1.485e+11p ps=1.56e+06u w=450000u l=150000u
X1 a_n33_n45# a_n81_n133# a_n125_n45# w_n263_n255# sky130_fd_pr__nfet_01v8 ad=0p pd=0u as=1.395e+11p ps=1.52e+06u w=450000u l=150000u

Extracted Spice with Flattening:

X0 vss B out vss sky130_fd_pr__nfet_01v8 ad=2.79e+11p pd=3.04e+06u as=1.485e+11p ps=1.56e+06u w=450000u l=150000u
X1 out A vss vss sky130_fd_pr__nfet_01v8 ad=0p pd=0u as=0p ps=0u w=450000u l=150000u

That's the default behavior for magic, which accumulates area and perimeter per net, not per device. You can get a better approximation by passing "-d" (distributed area/perimeter) to ext2spice.