Challenging array formula (useful for financial modelling)

Hi, I need to solve a problem in excel with an array formula but I don't know how. I have managed to do it using different cells (see example) but I can't reproduce this behaviour with array formulas. I need to do this because the output array will be then used in a bigger formula and therefore the calculation must be "self-contained".

It's difficult to explain the mechanics of what I intend to do but the example file is quite easy to follow.

My ultimate goal is, given an array of dates (say end of each trimester but could be any date as long as they are in ascending order), to calculate an array (for every collumn - i.e. end of period) which gives the percentage of the preceiding periods that has to be taken in order to have a cumulative number of days of 250days (being the date of the current collumn tha last of this 250 days)

For anyone who is accustomed to financial models I need this for calculating the rolling last 250 days of sales in a model where the ending dates of the periods aren't evenly spaced and might change at each run of the model (therefore there can't be any hard coding).

thanks in advance for any help and sorry for my english.

Please refer to the example which is easier to follow than my goofy english

Paolo