This mod is based off of the books, and in the books, balrogs were human sized. Wasn't Durin's Bane only slightly taller than Gandalf in FOTR?

I thought they were about twice man-height, which is still much smaller.

in the Physical descriptions section of Durin's Bane page on "The One Wiki to Rule Them All" says that he was "Slightly larger and taller than a Man," but on the page about Balrogs, it simply says: "Large, twice the height of Elves."

Then they're way too big in the mod

Keep them at their current size. Makes them more intimidating. Would the Hill Troll chieftain and Mallory Ent be as intimidating if they were only the size of a normal hill troll and ent? No. They would just be an armored troll and a colorful ent. The Balrog wouldn’t be intimidating if it were only 4 blocks high. It would be as tall as Gondor town walls.

Of course, this suggestion is about the skin, not the model. A new skin would look much better, and I like the idea of an overlay.

Of course, having things larger makes them more intimidating. But 4 blocks tall is still rather intimidating. It's still well over twice the player height.

It is twice the players height. About (or less) as big as a normal troll

No guys. Twice player height? ABout 5'5". Ish. The balrog, 10 ft? Ish? No. 

Guys, balrogs were DRAGON RIDERS. Fragons were HUGE. They would be pretty big to ride dragons almost like we do horses. 

But on the SKIN, yes, the balrogs would be more darkness, and a fire overlay would be cool

1 Minecraft block is equal to 100 centimeters. (~3 &1/3 feet). The player is 185 Pixels high. That's 185 centimeters. 185 centimeters = ~6 feet. Twice that is 12 feet / 360 centimeters. 3.6 blocks isn't too bad for a Balrog. In The Atlas of Middle-Earth by Karen Wynn Fonstad, she claims that Smaug was 18 meters long (59 ft) but it is unknown is it is canon or not. First Age dragons are said to be larger than Smaug, but size is not known (other than Ancalagon, who was massive) But for now, I'm rolling with 18 meters. A 12-foot Maiar riding a 59-foot dragon isn't too out of proportion.

But on the skin matter: The current Balrog skin seems very temporary to me. The skin 100% needs a revamp, as well as the mob size to accurately place the world of LOTR inside of Minecraft.