Strange that you find the 800ES harder than the EM2300 to get consistent, I would have guessed they would be about the same (to get consistency). Perhaps its just the newness of it?
I find it touchy to get consistent shots on the 820ES. If Im not paying attention they will come out too fast or choke up. If I am paying attention I still get varying results, but usually between 20 - 40 seconds each.
Its probably partly your grinder - at this point it may not have enough granularity on the notches to get in between the "too fast" and "too slow" pours. It may also be your dosing technique - how do you ensure you have the same dose each time? You can weigh it, or scrape it, or whatever suits you best. And finally the tamp - how do you make sure its the same?
I personally dont like the tapered basket bottom on an already small basket - I would be trying to use the Breville single wall baskets since they have straight sides. IMHO if you funnell the pour into a small outlet youre amplifying changes in grind/dose/tamp.
Hope that helps - good to see youre experimenting and not satisfied with drinking mud ;)