I really don't recommend upper entrances, the bottom board opening is about 10 to 15 times larger than the typical hive entrance in nature (even though the bee count and squar footage is relatively the samesize as a natural hive) and these large bottom boards can accomidate massive flights per minute - watch a swarm evacuate the hive in seconds and you'll get the idea.
I'm a little confused on your terminology, so I'll try to break down what I think you have. All hive boxes are "supers", you have deep (what I think you are saying are supers) medium and shallows: these are the three sizes.
So I'm not quite sure if you are saying you have 4 supers total (2 deep and 2 shallow) or 6 supers (2 deep and 4 shallow) or mediums if you use those. But 4 supers high EVEN 6 high can still make fine use of the normal unreduced entrance.
If the supers are drawn out and full of brood or food AND you already vent it by tilting the telescoping outer lid toward the back - then you might need to think about splitting up the hive into two MORE MANAGABLE colonies and this would reduce the traffic a lot.
Honeybees DON'T return from the field and walk all the way up to the top supers to store pollen, nectar, water or propolis - they pass it off to young worker bees just inside the entrance and these young workers do the marching up the hive to store the food in avalable cells.
This is an important part of hive communication - honeybees need to touch each other, pass food sources on, have internal storage plans: pollen in the corners along with drone cells for example, and nectar and worker brood in the center of the frames. All these "Jobs" are done through strong pheromonal scents from the queen and passed on from her, through her tending workers - it literally is important for touching NOT JUST SMELLING of the queen scent to pass physically from bee to bee to bee.
So walking the long walk from the bottom super to the top (or wherever the storage is being done) is an important part of the life-cycle and well being of the hive. I don't like to seeing supers OVER-STACKED though, it is an accident waiting to happen. Anything above or below the baseball STRIKE-ZONE is a "Back Injury" waiting to happen, so be careful with these tall hives.
IF you choose to make an upper entrance, then I suggest you make it AT LEAST the SECOND BOX from the TOP - not the top super - drill a 3/4 inch hole (no larger) and maybe glue a small landing board below it - again, I don't recommend an upper entrance, but if you do make one make sure it is in centered in the super front and make sure it is a super that is drawn out fully. You don't want an entrance in a super that isn't drawn out, it invites thieves and opens the hive to infestation of other insects.
Personally though, if I had a hive 6 supers high (any size super) I'd split it, giving" both hives" equal food and brood and equal drawn comb. If it were 4 supers high, I'd probably keep it like it is and NOT add a upper entrance - also do regular harvest of honey to make room for continuous foraging and help keep internal temperatures lower.
Honey is a very AMBIENT product - like a swimming pool, it slowly changes AVERAGE temperature (unless of course you have serious temperature swings over a short number of hours - but generally, it is a "heatsink" in the Summer time, holding the heat "in" and making large bee count the main variable in the hive when it comes to temperature changes.
This is why you see bearding on the outside of the box in the evenings, the honey temperature CLIMBS SLOWLY throughout the day time and by time EVENING COMES the honey is at its HOTTEST and forces the bees to evacuate the hive to keep a steady 95F or as close as they can maintain for brood rearing as they can.
So even though it is COOLER in the evening, the hive temp is JUST THEN reaching its hottest temp of the day forcing the bees outside. Then it "cools off" over night, the bees return into the hive and "during the HOTTEST PARTS OF THE DAY" the honey is just beginning to warm up again. It has a very slow turn-around time relative to the hottest hours of the day. I think this confuses a lot of people, it seems Bass Ackwards: you would think the bees would be outside during the HOTTEST part of the day, not the cool evenings. But if you were to measure the internal hive temps, you would see that the hive is hottest in the early evening, long after the air temps have dropped off.
Hope all this helped :)