You are making profits from a straight bet, but it is probably too early to claim a strike rate although it is looking positive.
It really depends on your allowable risk.
Also, considering the fact that your strike rate is not guaranteed, there is nothing that I could suggest to you regarding a staking plan in the format you describe.
I bet a similar way to you and this is the basic idea of what I do.
I keep a spreadsheet of the last 30 bets. I record the odds I get a horse for, which becomes my probability of the horse winning.
I have a base return of $100.
I divide the number of actual wins into the number of required wins for 100%.
I then divide the base bet into the previous percentage.
eg if out of the last 30 races, you needed 10 winners to break even, and you only got 6, your bet would now be to return $167. ($100/.6)


The danger with staking systems is that the longer a bad run lasts, the more up ********e creek you are. What I am doing is limiting a run to 30 races so your bet shouldn't get past double its original bet.

Please Note:

This will increase your return percentage because you are betting more on your winning bets. I would not recommend using any staking system unless you are capable of returning at least 95% on straight bets......
I only bet fixed odds, and only bet to return a figure. This is my recommendation only.