I am pretty sure it was not like this before. From my experience with regular award booking, if miles are "earmarked" for expiry (i.e. expire this or next quarter) they are used first. (i.e. not in a proportion/ratio of accounts in the pool). Actually, this is pretty logical since otherwise these pools would be totally useless: suppose you have 10k miles expiring soon and another pool member has 50K non-expiring. For non-pool members you can just book 10K flight and avoid exipry. If "ratio" method for pool redemptions is applied only 2k from expiring account will be used together with 8K from the "big non-expiring" account, leaving another 8k to expire.
But since I am planning to use my almost expired miles for " CO compensation" and it looks like it is handled by :LH and not M&M, I am looking for some first-hand experiences.