First off - do NOT buy that CA mount. It sucks ass.
Reason: it is not an uninterrupted rail. Lots of sights won't fit on it.
Secondly - If you're using a red dot sight a low mount WILL work.
Its not like the dot cant have a chunk of metal behind it (a small bit of your front sight).
It's fine.
Thirdly - buy this mount:
http://www.intrudershop.com.tw/show_...?idproduct=592
It is stupid solid and an aimpoint will clear your front sight with an L mount. In fact, those other mounts are visibly clearing the rear sight.
Most sights should be good to go.