Problems occur when you get high velocity in the molten metal, and it starts washing and eroding the sand mold.
You want a slow even fill, with no splashing, no waterfalling, and as smooth a transition as you can make from the bottom of the sprue into the gate.
Sometimes people use a horizontal runner off the bottom of the sprue, but it is not absolutely necessary.
I have not used the miniscus method, but I have seen others use it with great accuracy.
I will look for a photo of a guy that uses the miniscus only (no pyrometer) and you can see the surface finish he gets with his greensand.
I am not sure why you have a sprue on both sides.
One sprue and gate should do it.
Here is an example of the surface finish you can get with green sand, aluminum, and miniscus only.
I am guessing he used the riser on the opposite side to ensure a complete mold fill, but it is not necessarily required, especially if you have that riser above the center of your casting.
And I don't think you need the vent holes in the top of your mold, since you have that riser that will do the same thing.
Edit:
If you use a ceramic blanket furnace like the one in the photo below, be sure to spray on satanite to seal the fibers and prevent them from getting airborn.
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