The incline really does throw it out.
You can get it close enough for fine tuning by using the end of the muzzle as the height point, which means making a best guess of the height using a piece of card with a small hole covering the lens to allow you to focus at such short range. However, its still not good enough to compete with (at short notice). The only way is to shoot the ranges to be sure, then use the software to fill in the blanks with the proven distances you have, and tweak the input data until you come close enough. I cannot be bothered with this way of doing things personally
The tilted rail is a PITA for more than just CG on Steyrs. Having said that I worked a different way around the problem, which does not involve CG, but still allows software use to analyse the results. Still using the Steyr rail......but the scope does not follow the tilt, it is now closer to bore line angle to align the optical centre with POI at 27 yards. Scope mounts were bedded with epoxy. This loses much of the advantage of the tilted rail, but still raises the scope height to be comfortable for head placement.
I use the two other software pieces written by CG developer, called "realwordPOI" and "realworldCLICKS". They are just what the Steyr set up needs to get you pin point accurate with your settings if you have to start over after changing a scope/mounts/pellet.