Yes, that's why I said they are "braces", not "rear lower arms"". Per the BGB, there are 2 "rear lower suspension control arms" per side, #'s 1(locates the hub in relation to the chassis center line) & 2(the toe arms). The braces shown in the op's pic do indeed "triangulate" the chassis, not the rear lower control arms.They are braces that go between the two lower control arm fixtures on the chassis/subframe.
So call them rear chassis braces of lower control arm brace as you please.
They ´triangulate´ the two and are quite noticeable if the rest is nicely taught. I have the TRD braces fitted.
Here is a nice write up
Rear Lower Brace Install (MR2 Spyder / MR-S) – Driftopia.com