Whatever the cause, my basal needs have been higher lately. I've been fiddling with both dose and timing.
To tide me over in the evenings until my 2200 Levemir, I've been doing 2U-3U of NPH around 1800.
A couple evenings ago, after an unusually "normal" (in both timing and quantity) day of eating, I decided to skip the evening NPH. I'd recently had a few late-evening hypos, and I wanted to see how the Levemir would do on its own.
I:BG = 1U:35mg/dL
aspart = 1hr 15min duration
human = 2hr 0min duration
NPH = 5hr 30min duration
BG @ 2013 : 67 (corrected towards 90-ish)
So far... so good... (At this point, Megadeth fans probably would say "So what!"

)
A bit more than an hour later, I felt like my insulin levels had dropped below basal requirements; it's hard to describe, but I feel a certain lethargic and "bleah" way. I tested and corrected thusly:
BG @ 2126 : 124 (did 1U aspart + 1U human)
I thought the 1U aspart would correct nicely, and the 1U human would hold me until Levemir ramped up. Was I ever wrong! A bit later, I felt rather rotten, and decided to check.
BG @ 2302 : 196

(time for 3U of aspart!)
Ughh.
BG @ 0106 : 67 (corrected towards 90-ish and went to sleep)
BG @ 0756 : 78
Although this is but one [statistically-invalid] experience, my take-home conclusion was this: A latent dose of faster-acting 2U does not make up for an earlier 2U of missed intermediate. Once I drop below basal requirements for "too long", I
really start cranking out the glucose.