Lowest beatable limit?

interesting subject,

did a bunch of analysis, and here's what i came to (assumed a few more bets in the pot the lower the limit) ...

based on 5% rake to max $5 (is this standard? i don't really know)

at 2/4, rake = 2BB/hour per player
at 4/8, rake = 1.5BB/hour per player

now playing tight aggressive, you probably donate less than average to rake as you don't invest as much in the pot AND your winning pots should be higher (crash thru the max on the high side as you raise alot).

i have a few questions about the rake though,

on small pots, $30 say, what's the rake structure? generally (i.e. what are the break-points? do they take 5% of $40 or $2 as they can't take $1.50)

and how does the rake generally improve in 10-20? i realize that there will be fewer bets in pot (more $$$$ though) but i have no idea on how much the rake structure improves.

thanks in advance!!!