Easy.
You don't care a f.ck about reducing to 1 bar or any other useless gimmicks.
You get rewards from previous attempts until you get a full payout. You add them all. You evaluate how much resources they're worth using each unit ingame description. This is your bank to pay back.
Now you go on hitting positions. You finish them or chip them, down to 1 bar, or whatever. Nobody cares.
But doing so, you're losing troops. This is the one and only relevant point.
Calculate your losses value in resources the same way as you did for your rewards. These are your paybacks.
When your total payback is almost equal to your bank, then your next hit will have lots of chance to reward you a new full payout.
Then you'll aim at high level positions, in order to get a payout that's big enough, or you'll have lost more than you'll get.
Note : you can finish the ones you've chipped down to get the payout, it of course works allright.
However, in order to get somehting there, you'll have to be close enough to paying back the bank or even having paid it back already, or you'll get nothing. The reason is you'll be needing very few troops to finish them, meaning you'll be paying back almost nothing. So if you're too far away from paying back the bank, don't finish the chipped ones.
Instead, hit a fresh new high level one so you're sure to pay back the bank once and for all. Then, either you'll get your payout right now, or you'll be able to finish the chipped ones at last in case you didn't get it already. The reason is you never have 100% chances to get the payout, so having a way to try other positions for almost free is a good thing in this case.
They're more spare positions than anything else.
Actually, this is the one and only reason why chipping positions down to one bar could be useful, as you're often broke when you're striking the last blow. ;)
Of course, never hit a low level position, chipped down or not, when you're waiting for the payout, as you could get it, and it will be as small as the level is low. Low level chipped positions are to be hit only immediately after the full payout.
