This is not a problem, even with a full batten in the bottom position. It is high enough and limber enough (on my main). I'm able to flatten the sail extremly, or put a nice buldge in it easily.I like the bottom one partial to take advantage of the loose foot when you want draft in the sail.
On a side note, anyone about to buy/build a new mainsl for their boat. Consider two reef points. One should be about where the factory reef is (40%) and another below it (20% aprox.). It's a great option and the reef point I end up using the most.
Best Breezes,
SK