Front derailleur twist shifter replacement - from small to big ring in one click

Replaced front OEM Grip Shift SH-F3 barrel shifter with Twist Grip M25-7 shifter on Vintage consumer-type bike w Shimano GS100 and 3 chainrings (x7 cassette).

Mounting went fine, cable run is clean and clear. Backed off barrel a few turns and with shifter on “1” and slack taken out connected the cable to the derailleur. Minimal adjustment needed to the L limit. But the shift from “1” to “2” skips the middle chainring completely and takes the cage all the way to the largest, and there’s no apparent index adjustment – nor instructions or even a product listing on the website (it was an amazon purchase of a “Shimano-compatible” – please limit the chastising). I’ve reached out to MicroShift for support but no response.

I do find it interesting that the new shifter 1-2-3 markings are not equidistant – there is greater spacing between 1-2 than 2-3 which I don’t get. For what it’s worth no amazon comments similar to my problem.

In my understanding Shimano have massive market share and that the mass-consumer bike market is highly standardized in components, altogether suggesting I’ve done something wrong – that’s where you come in – even though the mechanics of these things aren’t rocket science.

Any advice would be appreciated.