This year, I will have twelve chances of winning.Did I say chance? nope, I said proportion.
You will only have eleven.
Each of our bonds has exactly the same chance of winning a prize, you must accept that by the fact that it's a random number drawn from a pool, right? If you don't accept that then there's no point in continuing.
Assuming you do accept that, by definition, if we both have [say] £20k invested, that means I'll have 240,000 chances of winning but you'll only have 220,000 chances of winning over the next year.
It's a lottery. Imagine there's a lottery to win a car and that lottery starts in January and runs through to December. Everyone who buys a ticket during that period has an equal chance of winning but by your logic, you'd have more chance of winning if you bought a ticket in December. This is exactly the same principle.