Blow-by is primarily a function of ring side clearance in the top ring groove....and that is a function of the weight of the ring and how hard it rams into the top and bottom of the groove every single time the piston changes direction, and how hard it hits for a given weight depends on how fast it is going M x V..and how many times it has banged into the top and bottom..
In short, cycles..
No2 ring is primarily an oil control ring and No3 is all oil control.. so we see the job falls to No1..The side clearance is important because the only way the ring can do its job or a) making compression and b) controlling blow-by is if the face of the ring is held absolutely flat against the cylinder wall..
If the groove is worn--as a natural function of cycles---then the ring doesn't get held flat against the cylinder wall: it flops kinda like a windshield wiper blade..And a little wedge appears from the face to cylinderwall...and the 70-80 bar of combustion pressure will "see" the face of the ring and push that ring right back into the groove and blow tight on by.
Oil has nothing to do with it..Weight, velocity material, and cycles.
Have you noticed over the decades how top rings have gone skinnier and skinnier and skinnier over the decades as engine speeds have gone up? On some motors from around 5mm down to 1,5mm?
Rod and main bearing clearance and top ring side clearance are three of the most absolutely critical numbers in any motor, but of those three, ring side clearance is the most inflexible.( rod amd main clearance has a MUCH wider range of acceptable clearance.. ..
0015" is fine, but 002 is Ok and depending on usage sometmes even .003" is fine-depending..
But there is no way around the hard fact that the ring must be square against the cylinder wall or you
will have blow-by.