When you consider water vs air cooled, try to envision the air flow on the fins as if it was water, and envision the uniformity of flow at all places at all fins and also that if the air passed a fin on the way there it's starting out as "hot coolant" and note how in the h_ll are you supposed to get flow on the air exit side's fins - then you go "damn I'm glad I didn't have to design that SOB". Then take water, where you can flow it any old which way you want, in or out of the base, cylinder side or head and the thermal heat capacity of the water is easier to manage in conjunction with flow rate than the myriad of varying thickness air cooling fins with inherent problems of (pre)heated airflow, and proximity to the burn. Then you go, ok, water's gonna work better. And it does. They went to tighter engine tolerances to go with the more uniform engine temp.
A professor once set me/us straight on that heat exchanger design was non trivial even just for same flow vs cross flow. We just nodded our heads, remaining no smarter than before. Now there's CFD programs for the physics but the vagueness of 2 stroke jetting and loading messes things up. I remember the onset of water-cooled dirt bikes. I had a YZ125 with the rad on the bars where the number plate should be. I bet air cooled engine design is nearly a lost art probably based now on old established designs. I once tried to figure out the performance of a cpu chip to heatsink to air to receiver fins thru metal to external passive convective fins. I kind of got it but it basically beat me and confounded me, I never got a confident answer to it. But I did learn that in convective cooling airflow is king and hence various shrouding designs abound. Shrouding can use airflow to compensate a lot. Just look at your lawn mower or a vw engine. The temperature increase of the air on it's way by is pretty small compered to the metal surface temperatures and I think that's the secret. Imagine a car in Death Valley and you could say there's hot, and then there's hot, how in the heck is my rad still getting it done with 120 degree air blowing on it? Well that's a bit different, tons of fin area on a lower temperature differential. I've poked a can of worms.... get back in there!
Sorry if I bored anyone.
Yeah, housebound again