Understanding statutory notice pay calculation

Workerbee999

I have received a statutory notice pay calculation from the Redundancy Service (because my employer went into liquidation and didn’t pay any notice) but I don’t understand the amounts.
How should the weekly pay amount be calculated? Would it include car allowance as well as salary? What about employers pension contributions that would have been paid had I worked my notice? 
 I had max 20 years service, but the gross entitlement stated (before knocking off money  earned and benefits in the period, or deducting tax and NI) is lower than 12 x the weekly wage - does this sound right due to some other required adjustments that I don’t understand or should I be questioning it?
When confirming how much I had actually earned during the notice period was I supposed to quote the amount before pension salary sacrifice or after it? My new employer only contributes 5% whereas the old one was 15% so in my new role I am putting an extra 10% salsac in to make it up. So my “gross earnings’ that would show up on a P60 would be lower. I don’t know if Idid the wrong thing as I used the value after salsac.
Thanks