Clarification on Coplanar Single-Ended Impedance Calculation

Hi,

I have two quick questions about the Coplanar Single-Ended option in JLCPCB’s online impedance calculator( https://jlcpcb.com/pcb-impedance-calculator ):

1. My signal will be routed on Layer 1. To achieve the 50 Ω result shown by the calculator, do I need to remove the solder mask? I am using Layer 3 (bottom) as the reference plane, a 42.39 mil trace width, and a 10 mil gap to the adjacent copper, which the calculator reports as 50 Ω (see attached screenshot).
2. The calculator displays a red thumbs-up icon next to the “JLC04161H-7628” stack-up (screenshot attached). Does this icon signify a recommended or preferred stack-up?

Thanks!