Top Riser-Mount for M&P 15-22

[jackliu239]

Hey everyone, I need you help I am about to buy

http://www.opticsplanet.net/barska-red-dot-scope-w-extension-tube-ac10326.html

and

http://www.opticsplanet.net/leatherwood-hi-lux-optics-1x30mm-red-dot-tactical-sight-es1x30tp.html

for my M&P 15-22, then I realize my iron sights will block out a large chunk of the view and I don't want to take them down, but I have no idea how high of Top Riser-Mount do I have to buy to mount those red dot scopes. Can anyone help me pick one out from here?

http://www.opticsplanet.net/riflescope-mounts-rings-and-bases-by-price-2.html

or just tell me how high of the mount do I need to buy please.

Thanks