Bare in mind that in Diamond division you will only be placed against clans that have exactly the same amount of members that you have when the rosters are locked 24 hours before the war starts.
If you would like to maintain a friendly yet competitive atmosphere then I recommend you do what I did in DD and make all your clan aware that if they cannot participate a minimum of 2 out of 3 days then it's within the clans interest to remove them when the rosters lock and re-add them after the war (Pro Tip: You can add them back as soon as everyone included in the roster lock has played their first match in an applicable node when clan wars becomes active). By doing this you will level the playing field and this will mean that those who participate will not be picking up the slack for not participating. Also that right there is incentive for people to show up for wars (commitments or not). Non active = No Clan rewards.
Also Your sub-division will always be pooled by size first and then afterwards by wins made during the last clan war (such as what the OP mentions)
