XF C6 Block Is Now My Favorite! Why The C6 Premium?

Got this about a month ago from Siegel. This is my favorite of all the stamps I own right now.



I am curious as to why the premium on the C6 block compared to C1-C5? The production numbers aren't that different? Is it just desirability? Was it actually in use more? I read the literature on stampsmarter about all the these early airmail stamps but didn't come across much as to why it would be such a higher premium.

Quick C6 Summary: The DeHavilland Biplane is pictured on this 24¢ airmail issue. This aircraft eventually replaced the Jenny in carrying the mail. This particular stamp was issued to provide payment for night flights from New York all the way to the Pacific Coast.

Quantities Issued(From scott)
C6 ~5.2M
C5 ~5.3M
C4 ~6.4M
C3 ~2.1M
C2 ~2.7M
C1 ~3.4M

Can't speak to blocks, but all the singles seem to sell for about the same (except C4, which goes for about 1/4 the others).

Plate number blocks can sell for more depending on the number and position.

All four of the C6 plate numbers (14840 - 14843) have the same value as per Durlands.
Don