When I was having difficulty with the bottom F and consequently trouble keeping my fingers on the lower notes, I was given the suggestion to first stabilize your finger positions down to the low G. Once you can comfortably play down to the G, then you can work out what’s the best position to go on and play the F. I found that by settling on one position for the foot, and working at that angle eventually I was able to play the whole scale. An exercise book like the G. Rooda Dexterity Exercises for F gives you a good many exercises that allow you to practice that way. Also the Sweet Pipes books for Alto as well. I hope this helps.
