Tailfin Setup Help (Sizing and Secruity)

Hey everyone,

I’m about to order a Tailfin AeroPack (Alloy) for my Ridley Kanzo Adventure Alu (Size XL) and need some final advice on sizing and security. I‘m a bit confused about the difference between XS , L and XL

My Stats & Setup:

Height: 190 cm (6'3")

Bike: Ridley Kanzo Adventure XL (Alu frame)

Seatpost: About 17–18 cm (6.7-7.1 inches) of exposed seatpost.

Usage: 3x/week commuting (iPad, gym gear, lunch) + weekend bikepacking.

My Questions:

Sizing (Rack & TopStay): Tailfin asks for the bike size (XS-L or XL). Chat GPT suggests the L (Standard) size for my setup. Has anyone with a XL Frane and similar height (1.90m) used the L arch? I want the bag to sit as level as possible.

Theft & Mounting: Since I commute to school and the gym, I’m worried about theft. I'll get the removable bag to take inside. But for the rack: Is the Frame Mount (bolted to the eyelets) significantly safer against theft than the Thru-Axle Quick Release? Or is the Axle mount much better for stability given the leverage on an XL frame?

Thanks!!