With a flat top and a properly mounted scope (you'll need high rings to get the scope up to about the heigth of the current rear sight) the front sight will indeed be directly in front of the scope. However it won't be in focus and will sort of disappear as you're looking far away at a target. If you try to focus on it you can. Thats the setup I have on my midlength carbine for the past 10 years. I never got around to getting a different gas block. If you're going through all the trouble pulling the barrel for a free float tube then you'll be removing the front sight base and you might as well put a rail type gas block on it. If you don't though it won't hinder your shooting. Heres a picture of my coyote gun with a $20 cheap ass walmart lazer I put on the gas block to see if a lazer will work with my night vision goggles for the 24hr coyote season (it does!). It is clearly at least as high as a regular front sight and I can't see it throught he scope unless I have it at 3x and pull back from the scope to where half of the scope has gone black from being too far back. Now I just need to order a good lazer to replace this one.