Today the "custom environment variables" are "all or nothing" between the layers, e.g. if you have 5 settings in "shared settings" and want a new one (or modify one) locally, you need to duplicate all 5 in "my settings" to avoid the other ones being "unset" in the test runner.

I would like "my settings" to only override the ones I specify, so I can keep the 5 ones in "shared settings" being "active", and only add (or modify) 1 specific in "my settings".