Hi Ingvar,
Thanks for your question. I understand exactly what you’re saying and it’s quite common for players to have this technique. Perhaps right now your coach is getting you to focus on grasping the spin production of the shot and not worrying to much about your technique for now. I would suggest to try and follow through towards your forehead, this will help with the spin in your strokes long term.
When you’re playing your forehand topspin make sure to be on the balls of your feet and move into position. If you have the ‘chicken wing’ style of forehand I think you will struggle to play from the middle when you are out of position.
If you can, post a video of your forehand via a YouTube link here. It will be nice to check it out and give you some further guidance.