I think its important to be clear about what ones' fire is and isn't designed to do. The concept for toplighting, I think has come from TLUDs ( Top Lit updraft gasifier stove) whereby small sticks can burn highly efficiently and very hot without evil emissions. So the average stove or wood heater is not be designed necessarily for this to work i.e. its not a TLUD, and whether burning from the top is a standard stove has any advantage is not clear at all. It is true that smaller fuel burns hotter and with less emissions so small fuel and a bright active burn helps.
I have an open fire, a well known brand but basically a piece of junk which burns with a lot of smoke, so I've experimented with top burning fires because of interest in permaculture and reading on TLUDS and biochar. I found that it really is much harder to get the thing started, but one started does burn reasonably well. What works the best, though, is a brisk fire with fairly small diameter wood i.e. up to 2-3cm in diameter. Its hotter and cleaner. The only problem is it needs frequent stoking. Prior to industrial saws, in England most houses burnt faggots* i.e. wood up to the diameter cut from ancient coppiced trees, bundled into a faggot for transportation. The advent of cutting down large diameter trees and the splitting them into smaller logs is a relatively recent phenomenon. This got me thinking about how silly it was to spend time cutting and splitting trees, when I have a ready source of small kindling and faggot diameter wood on my property, all I have to do is pick it up and break it up. So now I use a minimum of logs, which I use to maintain a steady mass of heat - one on either side and burn smaller diameter sticks in the middle - bright and fast. The big logs will keep things going if the small kindling just about goes out if I haven't stoked promptly enough.
* no rude comments please, I know what you're thinking..
