My spreadsheet updates after every race so on winning it allows me to bet more. On down runs it decreases my bets immediately. I think 'after every race' is the key. To not alter it until the end of the day means your either doing yourself out of decent money on a good day and of course.....alot to catch up if you realise at the end of the day its not been so good but youve been betting a higher stake then you should.

I think your right betting 2% win betting when your strike rate is lower. I kept a table next to my 5% place betting ages ago with a 10% bracket to see the difference. i found the 10% a bit too fickle.

Try this but alter the flat rate & profit rate until it fits as you like it (the 10% can be as much as 20%
>>> 2% flat rate + 10% of days profit added on top. Your staking more but the 'more' isnt extra out of your bank but a slice of what your already won. It makes winning days very lucrative. On losing days it makes no difference as 10% of $0 = $0 <<< so its just the usual 2% flat rate your betting anyway.
You can also drop the profit % right down as the day goes on to secure your winnings a bit tighter.