The plate and the little post are designed for a specific optic. If you use the correct plate for your optic, it'll fit flush.
From the Walther site.
The new Q5 Match from Walther is built for the production class competitive shooter. Built around our award winning PPQ platform, the Q5 Match features an optics ready slide that comes with a Trijicon RMR, Leupold Delta Point, and Docter Optics ready mounting plate in addition to the standard competition iron sights already included. Coupled with a ported slide, Carl Walther signature ergonomics, and a blue quick defense trigger, the Q5 is the firearm that gives you match performance in a production class firearm.
I'm thinking you may want to contact Vortex and explain your predicament to them. Seems as they may have some additional 'shims' that you might need.
Additional Mounting Options:
In addition to the supplied low Picatinny rail mount, other mounting base options are available for the Razor red dot. These include Weaver spec base rail clamps, custom handgun mounts, and riser mounts.
1. Remove the supplied Low Mount Clamp Base before mounting the Razor red dot to other bases.
2. Use the Mounting Shim (a custom adapter plate) when adapting the Razor to specialized red dot bases from other companies.