Top board function question

[Sundog]

I'm one off those people who likes to understand why and what for.  I like to understand how a concept works and what the principal is, and then I create my own variation, my way.

So, other than the obvious, what is the principal and concept behind the "top board"?  Do the bees not like it if there is too much or too little space over the top of the frame bars?  Bees seem so adaptable in the wild, building in all kinds of strange locations, but I realize established techniques have been researched to optimize production the and well being of the bees.

TIA

Have fun!

[Finski]

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There is a 10 mm gap between frame bars and inner cover. If it is bigger, bees seal the cover with burr. If it is smaller, bees will be crushed easily because of burr. I like bigger gap. 15 mm is good for me.

I use the gap when I feed in Spring pollen patty.

Many professional use plastic folio between bars and cover that burr does not glue the cover to bars. I like that  it is glued. Wind does not take cover away even if it takes the rain cover.

[VolunteerK9]

I think they also help to create an insulating 'dead air' space between the inner cover and top telescoping cover. The hole cut in the middle makes a great place to put a jar feed over for feeding, and the notch in the front makes for an upper entrance and ventilating hole. If one just used a tele top without an inner cover, the bees would propolize it down making it incredibly difficult to open. I have hives with inner covers and tele tops and some with just migratory tops.