Confused about sadaqat al-fitr

[Acacia]

I am a little confused about this and would appreciate some clarification with regards to the following:

1. is the amount 1.6 kg or 2.2 kg (in Ascent to Felicity 2.2 kg is noted as being half sa)?
2. Wheat and barley prices vary, they each have their own price and the price fluctuates. In Canada, the prices are usually quoted per bushel or tonne. 1 bushel of wheat = 27 kilograms, and 1 bushel of barley = 22 kilograms (I used the USDA conversion chart). Are we to calculate the monetary value by looking up the market value for the grain in our currency/country?
3. I tried this with the July 5th price (in US dollars) here and got $0.34/kg ($0.54/1.6 kg and $0.75/2.2 kg). That said, if I was to buy 1.6 or 2.2 kg of wheat at the grocery store, I'm fairly certain it would cost much more/kg (store's profit margin). If the point is to feed a person/day, is it better to donate in wheat, flour or barley rather than money?
4. In Ascent to Felicity, it is stated that: "It is permissible to pay by monetary value...; this is actually superior when one can find what he needs - i.e., in times of ease - as it is more expedient in fulfilling the needs of the indigent. If, however, it is a time of difficulty [like famine], then wheat, barley, or any staple good is superior to monetary currency." In most stores here, 1 loaf of wheat bread costs more than $1.00 Canadian so I am a little confused about the low amount and when it is better to 'pay' in grain/flour rather than money. Are we to take world famine into consideration or is it just our location? Even so, it seems more 'bread' can be made with 2.2 kg of wheat than can be purchased with $0.75 (1 standard loaf of bread requires roughly 450 g of flour) - does this reality imply "a time of difficulty," necessitating payment in grain rather than money?

[Acacia]

This thread is relevant here. Sorry, I hadn't seen it prior to posting.