If you slip as much as you move forward during pressing on the water you already doing fine, so everybody will be surprised if they hit a ladder at the side of the pool.
By reaching i dont mean entering the arm at the centerline. Just at 10 and 2 oclock.
Its moro about lifting the shoulder as much forward as possible, with a high elbow so the forearm and hand can be positioned in the right angle as soon as possible.
The shoulder is in tension in this position and wants to move back to its normal position. You let that happen when the forearm is angled right and let elasticity take care of part of the job. The stretch runs over the whole torso.
You are right that fishtailing can happen when going too far, but with increased flexibility the compromise shifts to earlier holds on the water. Accelerating to the end makes the longer ofcourse.
All together the same old stuff that has been talked about in the freestyle section before.
pictures tell the same old story again
I like to start out in kpns V, get into a rhythm and slowly try go move the catch more upfront untill problems arise, but arms never pointing to the centerline.
3 min 40. Bodyweight right on the catchpoint, reach, high elbow, very little slip to tiles. Best traction and acceleration at shoulder height.. (but she has super kicking technique too)