Cadence IC6 - layout instance/drawing box no longer constrains selectable extents

Ever since SDA2.0 I'd been using the trick of
placing a box on instance/drawing layer in a
layout, much smaller than extents and with
cellName text in it, to serve as the "one and
only selection handle". Very useful if you are
working at chip scale and your I/O ring is
always the first thing selected, like it or not.

This was fine up through IC5. Sometime
during IC6 era, it quit working. Advice about
the problem on CAD & Cadence sites seems
to peter out around 10 years ago, and is
currently wrong. That was, a variable named
"useTrueBBox" used to be nil (so use "found"
instance box, if) and got changed to 't' so the
natural extents are used. At or about this time,
instance/drawing and many other "legacy"
layers also got "disappeared" from PDK
layertables.

Later notes about properties on cells and
libraries refer to things that aren't there
today, that supposedly take priority over
the variable.

Anyone doing Cadence layout, and has figured
out how to re-enable the instance-box selection
constraint? It's way handy once you get to big
structures with overlapping instance extents.