Rollup Field over connections

Hello Everybody,

i use connections from accounts to contacts/accounts to establish ownership role for the specific account.

i customized the connection form and added a decimal field called ownership percentage.

i added to the account entity a decimal field with a type of a roll-up.

but when i try to choose connections as a source for the roll up field, it does not show up on the list.

is it not possible to use calculated/roll up fields on connection records?

thanks,

Tal