I had never heard of "medio tiempo" (other than the simple Spanish translation of "half-time") applied to tobacco until some marketeer came up with it for some cigars less than a decade ago. In Spanish-speaking cigar world, tip leaf is usually just called corona (crown).
"They also get the full benefit of sunlight..."
"On some plants, but far from all, two additional tobacco leaves grow at the very top, above the ligero. Those leaves are called medio tiempo."
"Medio tiempo is very rare. Some farmers estimate that fewer than one in ten tobacco plants grows medio tiempo leaves."
Any of you who have actually grown real tobacco know that these three sentences don't smell quite right. While it is true that tip leaf is smaller on some plants than others, every plant ever grown on earth has leaves at the top. Tobacco leaf nodes (where the leaves emerge from the stalk) are rotationally staggered as their growth meristems' locations appear on the growing stalk. Silly names for specific pairs of leaves is not meaningful. They don't grow in pairs. The leaf stem positions form a pentagonal symmetry (just like tobacco blossoms).
About getting "the most" sunlight, tip leaf often emerges from the stalk much later than lower leaves. Can't be getting sun if you're not there yet. Also the pentagonal distribution of all the leaves minimizes the shading from higher leaves.
If you top your plants well below the crowsfoot, then you won't see tip leaf. Otherwise, you can become an expert on the subject in a single growing season--a benefit not available to the folks who write articles in popular cigar magazines. "We interviewed a grower who sells Medio Tiempo leaf at an exorbitant price, and he said, while taking a puff on his $30 cigar, that it's truly rare leaf, reserved for only the most bigly premium cigars."
Sorry. I get carried away, when I read so much of the fluff written about cigars and tobacco growing. (for example, the well-published assertion that the Perique variety will only grow in Louisiana. "Others have tried growing it elsewhere and failed." [bullshit])
With regard to using tip leaf in a pipe blend, if it's a suitable variety, then it would make an excellent condiment.
Bob
(smaller leaves above the ligero) 
