Connecting both meters in current mode is tricky and not measuring the real offset of the current. Both meters can have a small input voltage offset. They are not made to work with a low impedance source, but a high impedance current source.
With both meters in current mode would measure the difference in offset divided by the protection / isolation resistors of both meters. Adjusting this offset to zero would be better with a simple short than a 2 nd meter.
I know the V7-45 is using a kind of integrator, but similar to an TIA it is a relatively low impedance (may be still in the 100 M range) input. With those small currents 100 M is considered low impedance
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The more relevant test would be having the V7-49 in voltage input mode, which I assume the meter would also support.