I've done many. Never had a leak.
The flange should be sitting on the finished floor. Sitting right on the tile, in your case. And it needs to be relatively level. Use plastic shims if needed and definitely secure it to the subfloor (not the tile). And the floor needs to be secure, not rotted or bouncy. You probably need shims between the flange and the tile if the flange won't go down when you secure the flange to the subfloor.
I often use 2 regular thickness wax rings stacked. The bottom one with the funnel plastic and the top one just a ring. I like to have with me 2 regular wax rings and one extra thick. With that I can find what will work. And I NEVER use the rubber ones. If it ain't broke....
But the way to see how much wax you need is to gently set the bowl on one ring and feel if it needs another. When you gently set the toilet down on the ring(s), does it stick up off the floor just a little? It should. If not, add more wax via a second ring or a thicker ring. You want the bowl to be off the floor a little so that when you push down it compresses the ring(s) and seals all the way around the ring(s). But just a little, not a bunch or you could crack and push out the extra wax. A very slight twist (tiny) when setting can help seat it, but not if there's shims - straight down. I sit on the bowl and kinda bounce myself to add weight. Then bolt it down.
All of this is after you dry fit the bowl to get it level, using clear toilet shims, pennies, dimes or nickels if needed. Which on tile, are nearly always needed.
By chance, is your flange secure to the floor or allowed to rock, or be pushed down? The plumbing is not designed to secure the toilet, which is often how someone leaves it. The flange bolted to the floor is what secures the bowl when it then gets bolted to the flange. The plumbing should just be coming along for the ride. But I cannot tell you how many "plumbers" leave the bowl to be secured by just the pipe.
Like I said, never a leak and I've done countless toilets. Additionally, if you caulk the bowl to the floor after, leave a small uncaulked portion in the very back so that if there ever is a leak you will see it when water leaks out the back.
I never use anything special. Just either 1 or 2 regular thickness rings or 1 extra thick. Mostly depends on how nice a job the bowl casting was and how high they left the flange. It is supposed to take one regular thickness ring if the flange is sitting on the finished floor. Many times it is sitting below the tile and on the slab or up off the tile partly & tilted. Btw, is the bowl outlet porcelain in good shape on your bowl? It should be nice and clean and not chipped or otherwise boogered up. Cheap toilets can be "wrong". I refuse to install crap. No pun intended.
My procedure: After everything is clean and not boogered, I bolt the bolts to a secured, level-ish flange. Then, after dryfitting, leveling (leaving the shims on the floor) and marking the outline of the bowl and shims on the floor, I set the ring on the flange. Then the bowl on the ring. If it's sitting up to my liking, I then weigh it down to seal the wax, bolt it down and then install the tank. Plumb it. Check for leaks. Then the seat and caulk with Dynaflex Ultra or 230 (water based). It takes me about 45 minutes to an hour to switch out a complete toilet. Longest on tile because of the leveling (maybe even 1.5 hours then). And when done, it's perfectly level, straight and leak free. I have, however, seen rough-ins that were so bad that I've had to epoxy-repair flanges / slabs.
Hope this helps. Let us know.
I should clarify that the "sitting up" when feeling for how much wax you need is that you are just trying to "feel" if the wax has made complete contact with the bowl outlet. The wax and the outlet are unlikely to meet perfectly so the little bit you need is so that when you push down on the bowl it will compress the wax and make up any gaps from imperfect mating. But not so much that the bowl is off the floor any real measurable amount. As I set the bowl down, still supporting the weight myself, I can feel if it's made contact enough. Just touching the wax won't do and sitting up off the floor where I know it's gonna squeeze out the wax won't do. I want contact and compression. Not a gap and not a squeeze out. Also, the wax needs to not be cold. In Vegas, that's never a concern.