One BR for Various Stakes

I was thinking how i should manage my BR if playing various stakes.

I started playing $1 to $5 buyin MTTs.

For now i have a bit more than $150 in my BR which makes playing $5.50 MTTs incorrect for my BRM. I'd love to have at least 50 buyins. But as i do also play $1, $2 and $3 MTTs - should it compensate a small BR for those buyins of $5?

Let's take it this way. I do not have any sample yet, but i feel like i can achieve a ROI of something like 100% for a start (we can assume ITM of 20-25%). So, if i lose one $5 buyin and i play one trny for $1 and one for $2 i am expected to win $+3, which makes my net loss to be only $-2. Then it seems like BR of $150 is not so bad.

Or am wrong with the math?

PS. please, don't ask me how can expect to win anything if i have no personal stats