WAAS works pretty well in that area actually. Used it on 430 for 4 year there
How would you know that? The only way for you would be to go to the satellite status page on your Garmin unit and see if you can see WAAS satellites plus you should see a status like "3D DIFF NAV", plus letters "D" under individual satellite bars meaning that differential signal is being applied. Your manual would tell you what to look for. Without those signs there is no WAAS, just normal GPS.
Whether your Garmin 430W is compatible with European EGNOS system (which is much closer) - it is a separate question.