I have been windsurfing a couple of years ago at the "presqu'ile de giens" nearby l'Almanarre & Hyeres, with 35+ wind coming from the east (vent d'est, no Mistral) also on-shore. I'm 87kg and needed a wave board of +/- 86L and a sail of +/- 3.7m2 and a small wave fin of max 25cm. All other equipment was too big to handle that day.
I still remember that I also had problems with the nasty shore break (continuous series with little spacing in between) that kept on sweeping me back onto the beach. Then there came a guy to me, who saw that I was struggling, and told me to swim a couple of meters with my equipment just behind the shore break and waterstart over there. From then on, it went super. With strong on-shore wind and a nasty shore break, you need a little space (especially with small wave sails) to go a little bit down-wind into planing and then point again towards the wind. I've seen experienced wave windsurfers struggling that day as well and doing exactly the same thing.
Hope this helps.