Most people tend to play open chords in "cowboy position"; that is, the back of the guitar neck rests more or less in the palm of the hand and the thumb wraps around. When we play barre chords we usually shift to "classical position"; that is, with the thumb planted squarely on the back of the neck.

The open position F chord isn't really an open position chord - it uses no open strings - and the bar with the forefinger on the 1st and 2nd strings makes it very difficult to play in cowboy position. The only way I can play the "open" F chord is by shifting to classical position as if I were playing a barre chord. Give it a try - you might find it easier.

Mark