its interesting you say you get better success in soil with bigger clones, i find the total opposite to be true, some of my clones are only an inch high above the soil line, this way they cant wilt as the stem is not long enough to lean over, i always take small clones now and get 100% success in soil, so i guess once your used to one method then that method is always going to work.
i prefer to clone direct in soil as i grow in soil so using a bubble cloner means i need to stress the roots when i transplant and i did lose 2 clones after transplanting from bubble cloner to pots so i only used that method once, for me soil is the best way to go and if i can take just 1 cutting and root it everytime then its all good.
how ever their are some strains that just wont root at all, i took about 15 cuttings from one plant and everyone kept dying and i couldnt work out why, then i read that some strains wont root even when you take the clones in early flower when N is a bit lower. so i had to try something else as i wanted to grow it again, so i read my european grow bible and came across air layering method, i gave this a try and it worked, plus with air layering the clone can be as big as you want it to be, you could clone using a 1ft side branch.
air layering will work everytime as long as you keep the area you want roots from covered so no light gets in, once you see roots growing out the medium just cut the cutting off the plant and your good to grow.
then theirs soil layering which ive never tried, basically you have the plant your taking the cutting from then on top of the soil you place a small pot so that you can pull one of the side branches down and bury part of the stem in the new pot, then scrape back the part of the stem that will be planted below soil level and apply rooting hormone, then bury that part in the smaller pot and leave it joined to the parent plant, within a week or 2 their will be roots growing in the new pot so once you see roots when you gently dig down you can cut that branch off the mother plant and take it away in its own pot, the best things with air and soil layering is the cutting dont stop growing while its rooting as its still attatched and being fed by the parent plant until you cut it free once you know its rooted