Everyone is free to set whatever standards of safety for themselves as they please. If you choose to "push your batteries", that's on you. You are aware of the risks and you accept the potential consequences.
However, on a public forum many novices come here to ask questions specifically about safety limits. As veterans, I believe it is our responsibility as a community to educate these newcomers to practice on the "conservative" side of the line for their sake. Staying within their battery's continuous discharge amp rating is considered to be the standard on this forum.
Ohm's Law. I don't understand it entirely, but I can easily determine what is "safer" by using a simple ohm's law calculator. Know your battery's true amp limit (continuous discharge rating, not the useless "pulse" rating) and know the amp draw of the coil. Don't exceed the amp draw with the particular battery you use. It's simply that simple. That's the only two things we need to know about Ohm's Law.
Concerning the battery orientation question, I believe the user should orient the battery according to what the mod manufacturer recommends. If the product description doesn't say, contact the manufacturer. Some mods are designed for the + end to be oriented towards the atomizer, while others are designed for the + to be oriented towards the firing pin (bottom).
Vent holes? I just hope that the mech has some at all, because I see so many with NONE. That is literally a pipe bomb waiting to happen. You're a fool if you use a mech that has no vent holes, IMHO.
Are top vent holes or bottom vent holes preferred? To me, it depends upon the battery orientation. Batteries are actually designed with a weak spot under the + end to allow venting to best avoid the battery from exploding during early battery failure. IMHO, the vent holes should be located near the + end of the battery (where ever that is) because that is where the hot gas will accumulate first. I would not depend upon the gas traveling the length of the tube if the holes are in the other end -- the insulating wrap and battery cell can swell/expand in size blocking access to the vent holes. Some manufacturers leave no space in the battery compartment to prevent battery "rattle". Then you essentually have useless vent holes and an enclosed metal tube.