Some time ago I started using a 10 oz pitcher, since I usually pour one milk-based drink at the time. Initially I thought I was getting a nicely textured foam with good control, until I found the tip holes were gradually clogging up, so slowing down the froth and giving a false sense of control. Since I unclogged the holes the window of opportunity for frothing has obviously been shortened a lot and ever since I haven't been able to get foam to remain on the "canvas" that is the crema. After I have swirled and knocked the pitcher I get what seems like well-textured microfoamed milk with wet paint look and all, but when I pour, everything dives underneath the crema and no foam surfaces, even later during the pour.

My question is: Is it possible to "overswirl" so that the milk/foam mixture becomes too homogeneous and does not separate the foam from the milk during the pour or should I be looking for a better pouring technique? I use heat-treated whole milk, with which I have been successful previously. I am not talking about mastering latte art just yet. First I would like to get a decent cappuccino classico. Sorry I am not able to back this up with a video showing my routine, but any tips / tricks are welcome.

Perhaps pouring technique? How close to the cup are you pouring? Generally the higher up the pitcher, the more the milk/foam will sink to the bottom. The lower the pitcher (closer to the surface) the better it will sit on top.

How close to the surface of the crema is the spout of the pitcher? To high and the momentum will carry the microfoam under the crema. My spout is around 1cm or less away from the surface when I want the crema to surface. For a classic monk cap you can texture longer to get a stiffer foam. You could also plug one hole on your steam want to slow down the process.

The BZ10 machine also has a ball valve like my elektra. With some practice you you can partially open the valve to get longer stretch times as well. It does not have to be all or nothing. I do that when I am steaming 3 or 4 ounces, and it prevents the milk from blowing out of the pitcher from the steam pressure.

I usually start pouring high (some 4-5" above the rim) and end low. My cup of preference is a 200 cc double wall tea glass to pour into, which is higher and more narrow than a classic cappuccino cup. I will try to start off closer to the rim, see if that helps.
I have never tried it, but I am not aware that you can lock the joystick of the BZ10 steam valve partially open. I am away from home until tomorrow evening, I'll give it a try then.
On a few occasions I played with commercial gear (Spirit, LMLM) and did get a monk cap (using a bigger pitcher, that is), so why I can't get it on a BZ right now is a bit puzzling. I remember seeing a David Schomer video where he claimed only a 4 hole tip will texture the milk properly. I am using a 2 hole tip, but I don't think that should be the issue. Thanks for the replies so far folks.

If you want a monk cap and you are having trouble getting stiffer foam when you froth, try letting the frothed milk sit in the pitcher without swirling for a bit to so that the foam and the milk separate. Then try to pour.

You can also keep the pitcher in the freezer and pull it out when you froth to slow things down

If one "stretches" the milk until too hot a temperature, the texture of the milk will suffer as you describe. Probably, your milk has a slightly grainy texture. This can mostly be solved by allowing the milk to sit in its pitcher for 30 seconds or so, swirling occasionally to keep the foam from blobbing up (technical term) on top.