Non dwarfs suck.

If you have no idea how the dwarfing gene works I highly recommend doing more research especially if you're interested in showing Mini Rex.

a Dwarf rabbit's dwarfing gene looks like this Dd
a Non dwarf looks like this DD
a double dwarf (fatal, peanut) looks like this dd

So breeding a non dwarf to a non dwarf you will only get non dwarfs (nothing showable). Breeding to a dwarf, you will never get peanuts, but 50% of your litters will be non dwarfs and therefore not showable. Breeding a Dwarf to a Dwarf you do get peanuts 25% chance, you also have a 25% chance of non dwarfs, but a 50% chance of dwarfs which are showable*

Non dwarfs: We refer to these as Big Ugly Does (Buds) and Big Ugly Bucks (Bubs). For the reason that they're big and the lack of a dwarf gene tends to elongate features making them "ugly". A non dwarf is too big to be shown, and will never contribute a dwarf gene ever. Although people do try and pass them off as show quality by saying they have "summer ears". Summer ears is a term used to say "This rabbit has ginormous ears and is obviously lacking a dwarf gene but I'm going to pull the wool over your eyes claiming temperature can change genetics and sell it to you for double the price it is worth because you don't know any better."

The size of a rabbit's ears is determined by genetics and whether not they have a dwarfing gene. Rabbits with a dwarfing gene tend to have ear lengths under the maximum for the breed, and the exact length is an inherited trait. Not all rabbits with a dwarf gene have the same length of ears. Rabbits lacking a dwarf gene tend to have ears over the max length again exact length varies with it's genetics.

Extreme temperatures are not going to override genetic maximums. A rabbits ears are the first thing to reach maximum length. So for a time the rabbits ears will look out of balance with the rabbit however with a Mini Rex they should never be over 3.5 inches especially in a young rabbit. Saying heat will make a rabbit's ears grow freakishly long will also mean you will only get freakishly short ears in the winter. Which definitely is not the case.

In some cases people like to keep does with no dwarf gene because they do have larger litters. Personally I do not see how this is beneficial, you just have more kits born who are unshowable and slated for the pet market which gets you nowhere in your breeding program. Big bucks are just no. You shouldn't buy them you shouldn't breed them they're just big and will crush your does, and they'll hate you for it.