I am sure that it is possible to have multiple porosity types on your head--hair is supposed to increase in porosity when it is damaged.

For myself, I certainly notice that my somewhat fried canopy dries a lot faster than the underlayer (though to some degree that's true of everybody--the canopy is exposed to air, after all); however, even it seems to retain low-porosity characteristics: still pretty slow to dry, tough to get it to absorb products. It sounds to me like your hair may be lo-po through and through, but it behaves differently based on whether it's "virgin" lo-po or "damaged" lo-po.

Slow-drying ends would make sense. Your hair is holding onto all that water instead of releasing it into the air--it's just gravity that a disproportionate amount of that water ends up in the tips. My roots are always dry way, way, way before my ends.

Re. your roots, are you a co-washer? Working on your technique may help get them saturated in the shower. You're supposed to vigorously massage your scalp/roots with the pads of your fingers. With the right co-wash, that should lift the cuticle to get both water and moisture in.
Jessica
Type 2c: coarse, high-density, low porosity (so it would seem)
Avoiding protein and glycerin; going for soft, non-crunchy, frizz-free waves
CO & RO: Tresemme Naturals Moisture
Sealer: Olive oil
Leave-in/Styler: Kinky Curly Knot Today
DT: olive oil and honey