In article ,
"Richard D. Saam" writes:
In as much as lensable mass varies with universe density ~H^2/G (1+z)^3
then "high-z lenses will to be more powerful than low-z lenses"

I don't understand this. Lensing depends on the contrast between
high and low density regions, and all standard models have that
contrast _increasing_ with time (i.e., larger at low redshift).

In any case, what is needed for the test the OP proposed is not an
average mass or mass density but known mass for specific lensing
objects and different redshifts.

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