Final table Blind structure???

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Our local B&M weekly $100+15, one $100 rebuy usually has 4 tables. Almost everyone rebuys (800 chips to start, 1200 for the rebuy), so there is on average 80,000 chips in play. When we get to the final table, the stacks will usually range from 1000-20000 with the average at 8000.

With 20 min levels, the blinds rise so rapidly that it seems the three hours of previous play becomes completely moot and an all-in crapshoot takes place. We were 7 handed last night with blinds at 1000-2000 and then 2000-4000.

Any thoughts on this structure? Is there a ratio of aver chip stack to blind size that allows for more play in this situation?