I had trouble finding anyone talking about being able to foil on the sound before this year's trip. Real Watersports brags about having the rare sound side depth...but of course you can't launch from there. I have never worried about depth because of twin tipping of the past. We stay right on the sound so really didn't know what I would be in for. I also didn't want to mess with short masts....I wanted to use my main gear. For future reference the sound side of Avon is totally doable. Vorace so just over 1m in depth....quite a body drag out but once out it has been great....and even if you do venture to close the depth changes so gradually that its a gentle scrub when you do hit. The further north reaches are over head deep. You can see my GPS plots in the photo link below. The tide swing helps a bit (refer to tables) but its not a big change.
https://goo.gl/photos/ej7k85AWvjjXWTkV8