In my betting I bet only when the available price is greater than my assessed price.

If it boils down to only 2 possible bets,should I put a larger bet on the game with the larger overlay or the one that I assess as most likely of winning?.

Or you could just flat bet...

Problem with the large overlay, is while you think you may have a greater edge, it may be you just overlooked something the bookies didn't.

An example is AFL round-7.

I pick Essendon by 33 pts which I consider to be a $1.20 chance.$1.25 available.

Sydney to win by 40 pts. which is $1.15 and there is $1.20 available.

Both bets are equal overs,but my margins tell me that Sydney is the better bet.

By betting to my percentage chance I would in fact have slightly more on Sydney.

In reality the overs are too small,so I won't in fact be betting here but I do have St.Kilda to win by 17 points which equates to $1.44 with $2.10 being available.
This could be the situation where I may have overlooked something.

Have you recorded how all of your opinions have gone? If you think something should be 1.15 when it is 1.20 why wouldn't you bet? I understand that alot of people like a larger margin (a bit of a buffer) but the thing is if you are more accurate than the bookies the bets will be profitable over time. You are right that it doesn't give much (any) room for error, so unless these bets have shown to be profitable you should leave them alone (which is why you should record them even if you don't bet them).

I'd just flat bet. You don't really know how much of an adge you really have on either bet so you'd want to be conservative.

If you don't bet the 2.10 you should still record it. If I was you I'd try to develop a system based on what your normal thoughts are, where you look for advantages etc. Test it over a few years of results.

I'VE GOT IT !.
You only win in proportion to the amount of overs you received.Regardless of what it says on your betting slip.
If you are constantly betting when you have a 10% edge,then you will make 10% profit over time whether your selection is rated at evens or 100's.
It is when your perceived edge is wrong,that you will in fact lose over time.
There is powerful knowledge in these words for men of understanding.