You need to put it behind the turrets so you can lift your head and see it. The commercial one you posted flips up so you can see it when you have your head down on the stock. I have a couple of these
which look pretty good
but the level on the turret is not the best way to level your reticle because the turret could be off (most are). What you need is the EXD device
that has v-grooves that fit on your rifle barrel and the scope objective
and align your bore and scope while it levels your rifle so that it is not canted.
Even then your scope could be rotated in the mounts and your reticle would not be level. Best to aim at a horizontal or verticle object at distance (I use a 4' level on a fence at 25 yds while the rifle is in a vise) to level your reticle while the EXD device is level and your anti-cant device on your scope is level. Then you have it.