The rise in temperature isn't just the expansion of the cluster, it decreases the life of the bees. So as little disturbance as possible is the best bet. This means, everything is prepared and ready to go before you lift the lid, no splitting of supers from brood and a half, or splitting of double brood boxes, and quick effective tricking of 5ml per seam
evenly spread all along any occupied seam.
Observe bees, trickle, move to next seam, observe bees trickle and so on. If it drops directly out of the hive onto the floor then
it simply doesn't matter. Oxalic acid is cheap. With a 50ml syringe an effective but not excessive dose is achieved very quickly this way, squeeze to the next graduation mark, then stop.
You refill the syringe to 50ml for the next hive and you're all set to go again without mucking about worrying about what mark you were up to last or refilling halfway through. Of course if you have more than 10 seams of bees in your hive then you are buggered, but then you really shouldn't have clusters that big now
Pissing about with '3.5ml' over just the bees in a seam as some have suggested (here?) or in some of the mags is IMHO a waste of time.