What Will Acronis TI Home 2011 Do in this scenario

I have an old internal hdd setup as the ASZ. The HDD is 30gb. The Full backup of C is about 16gb.
I have setup to backup 1 full, followed by 15 incrementals.
On about the 5th incremental backup, the email from ATI 2011 states overwriting oldest backup. I wanted this if the ASZ runs out of space.
What will it do here?
Will it overright what is probably the only Full backup in the ASZ and leave me with nothing but incrementals?
I have a fullback weekly to external drive, but I wanted to know what Acronis does in this situation as I set it up on a PC that is for someone else and I am not there to look into ASZ and see.