I am using a full synthetic, and I do have near to nothing experience with non-synthetics and gas. So far, I have seen zero tendency to clog up the muffler nipple with the Oil I use (Castrol PowerRS 2stroke), but in the pre-solenoid days, the "blackening" of the fuel in the tank was a serious problem.
If I would go to the field with half a gallon of fresh fuel, do 2~3 10 minute flights and defuel the plane back in the fieldcan, that fresh, bright red fuel would already darken significant. Two afternoons and the fieldcan would be black. And consequently, running that blackened fuel through a feltclunk would restrict flow within a gallon or two per clunk. Not encrusted, just a discoloured clunk that would not pass sufficient fuel anymore. The craptraps were not installed to protect the fuel tank of the plane in question: their purpose is to keep the fieldcan clean, because for me it is imperative that I can defuel my planes (otherwise they stink up the house). Otherwise the "blocked clunk syndrome" would spread over my other planes like the black plague.

Post-solenoid, the blackening is less, but there is still the issue with the condensation of water from the exhaust gas in the fuel tank of the plane, and that appears to worsen a bit from the solenoid, since leaner mixtures cause the muffler to remain cooler (I have seen liquid water come from mufflers at idle).

For reasons I cannot explain, the few customers I had that were running Stihl alkylate fuel and Stihl oil, I never managed to get the engines adjusted consistent, not with and not without the solenoid. Same for premium fuels (98 RON rating)
That could be me, but I have consistenly had the best results with the simplest pumpgas (95 RON, comparable to your 91 MON. Over here it contains up to 10% Ethanol, which still has to show its first disadvantageous property yet, I haven't noticed any***) and this Castrol oil. I have tried Motul, and the engine runs satisfactorily, tunes well, but the residue is markedly different (gummier), and I have used the full synthetic sold under the brandname Q8, which behaves very similar to the Castrol.

As for mixing ratios, I have myself only experience with 10:1. I have tried 15:1 in the smaller engines, and it somehow "did not feel right"... Hard to explain, but I only used that for 2 afternoons or so, and my impression was that the engine was less well overall lubricated, did not feel as "wet" and I thought "this can't be right"

I have seen a few engines that were operated on 20:1, and I was not impressed. Internal inspection revealed that lubrication absolutely was adequate, but the dirt on pistoncrown and valves suggested less than stellar detergent action.

It is very possible that the clogged nipples you encounter are due to the relatively low oil content, but that is a total guess. But since I am not seeing ANY of that at 10:1 ratio supports that guess. But I do know that anyone that had issues with the special fuels or the lean ratios, would see improvement from using a good full synthetic at 10:1 in regular unleaded. It simply works better. Sure, there are people that get 20:1 working, or that have good results with alkylate fuel, and that's OK. But IF someone encounters issues, my goto-advise is a a craptrap, a clean feltclunk, a viton clunkline IN the tank, full synt oil 10:1 in regular unleaded, and start from there.

I think a (partly) blocked nipple and feltclunk after 200 flights (which is what? 4 gallons of fuel?) would qualify...

The one thing that leaves me baffled to this day is that you manage to achieve decent needle settings on standard carbs. I never managed that. A few of my engines were "flyable" but the poor throttleability of the engine spoiled the fun. The rest of them simply were "unflyable", because it becomes very hard to land if the engine won't follow the throttle with at least some consistency.

*** E10 fuel HAS shown very detrimental effects in my old carburated Ducati, both WRT throttle response and adjustability, as well as with corrosion and deposits in the floatvalve, acccellerator pump and carb jets. I can completely negate that with a relatively very cheap fuel additive (less than 3 cents per treated litre), and that seems to cancle all the negative effects completely, but the converted glow engines never needed that additive and do not seem to benefit from it either.