The finiteness-length formula for Abels groups over infinitely generated rings

Let $R$ be a finitely generated commutative ring with unity that is infinitely generated as a $\b7\mathbb{Z}$-module. For $n\b7\geq 2$, let $\b7\mathbf{A}_n(R)$ be the corresponding Abels group and let $\b7bphi$ denote finiteness length; write $\b7\mathbf{B}_2^{\circ}(R)$ for the indicated subgroup. Finiteness-length formula.

$$\phi(\mathbf{A}_n(R))=\min\left\{n-2,\phi(\mathbf{B}_2^{\circ}(R))\right\}\quad\text{for all }n\geq 2.$$

This would determine the finiteness length of these Abels groups in terms of the rank parameter $n$ and that of the corresponding subgroup. The surrounding discussion presents it as a natural problem and cites lower-bound results and examples, but does not state that the formula has been proved or disproved.