In humans, the percentage of nephrons that having long loops is:

The convoluted proximal tubule straightens and the next poion of each nephron is the loop of Henle. The nephrons with glomeruli in the outer poions of the renal coex have sho loops of Henle (coical nephrons), whereas those with glomeruli in the juxtamedullary region of the coex (juxtamedullary nephrons) have long loops extending down into the medullary pyramids. In humans, only 15% of the nephrons have long loops. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 37. Renal Function & Micturition. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.