My MTB is a B'Twin Rockrider 8.1 which I've had for years and absolutely love. However, recently I've been riding more and have noticed that I'm often perched right on the back of the saddle, which is as far back as it will go on the rails (even beyond the 'max' marker). Does this mean the bike is actually too small for me? I'm 5' 11" and the bike is a large size, so theoretically it's the right size for me. Are there any adjustments I could make to stop my bum constantly hanging off the back of the saddle? The stem is 100mm so I would guess fitting a longer stem is not an option? Wider bars maybe? Tilting the bars up?