I have some questions on rocket mass heaters

I'm early into my first build of a RMH and have some questions. I only have main internal workings so far to tune it in, no barrel or mass yet. It is a 6 inch system that somehow I missed that it needed 4 inchs of insulation around heat riser. I only have 2 inches. It draws very well and seem to burn pretty clean. I have only have 4 inches of insulation around the bottom of riser, this is all for testing purposes for now. Had to make some adjustments to get tunnel in riser (side) and burn chamber and feed the right size. The riser is hot at the bottom and not so hot at the top. Is it suppossed to be cool as possible? Is another 2 inchs of insulation necessary? Or will this bite me somehow? Can add another 2 inchs of insulation if needed. Also, I've been lurking on this site trying to soak up as much info. as I can, love it by the way you guys (and girls) are the best!. So much knowledge at many things. Also, I've read some things that are conflicting to me such as, you need to insulated burn chamber very well but I've seen Paul mention something about letting burn chamber cool down so you won't have conflicting cheminees on one of his video's. Would one of you intelligent people set me straight? Thanks

Also, can you put something like stove bolts (round headed), or a round thin steel ring on bolts for correct spacing so to speak, into top of heat riser to get the correct distance from riser and top of drum? Of course you wouldn't let the weight of drum hang on them, and then pack your cob around bottom, or would this cause holes to burn through drum or block flow? I'm asking because I relize how important that distance is. Or by careful measuring is it not that difficult to achieve. I don't want to make it harder than it needs to be, but I want it to be as close to correct measurement as possible for best performanace. Thanks