Potential hypothesis here:
Crazing happens when the COE of the glaze is greater than the COE of the body. BUT..... even if the COEs of the two differ, there has to be enough strees induced in the glaze layer so that the glass can't "stand" being in that amount of tension anymore (glass tensile strength is exceeded) and the glass cracks to relieve the stress.
When the COE of the body and glaze is close to the same, but still mismatched......... the glaze WILL eventually craze. It just takes time and other stressors to precipitate the crazing. The common ones are thermally induced... as in when hot liquid is poured into cups, hot food is placed on plates, sunlight is impacting on exterior tile installations, etc. .
So pieces that have this COE mis-match can still come out of the kiln looking just fine. No crazing. But the glaze is still in tension.....and is waiting to let go. The customer will be the one to see the crazing eventually.
Now when the glaze layer is very THIN, the stress between the body and glass is a bit lessened. There is less glass to be in tension when compared to the body. The stress is still there...... but the magnitude relative to the fracturing point of the glass is below the threshold. So it holds together (for a time).
So now we look at the cast mugs.
The wall cross-section for the general mug is pretty thin. So at a given bisque temperature the absorbency of that thickness of section will cause a certain thickness of glaze to adhere for a given dip / pour of liquid glaze slurry for a given amount of contact time. BUT... the HANDLE area is far thicker in cross section, being a solid cast and being in addition to the wall section at the attachment points. So it is possible (highly likely) that the thickness of the glaze layer in that area is greater than that on the rest of the overall mug. If you are holding the mugs upside down as the glaze drains, then the lip area would be a bit thicker deposit also.
In that area the thickness allows the crazing that is going to happen to show up first. So it is noticeable to the potter.
For making functional ware....... here's a suggestion to test the fit of your glaze to your claybody for crazing. This is a bit of a standardized stress test. Take a few fired sample pieces and pour boiling water into them. Empty them out after a couple of minuites. Immediately place them in your freezer for a couple of hours. Take them out and pour boiling water into them. Repeat this at least 10 times. Use the india ink test to check for crazing. If they haven't crazed by then......... the glaze and body fit each other.
Firing a glaze to a higher or lower level of heat work (cone) can change the COE of the glaze. Could be part of the issue. All cone X glazes are not of the same chemical formulation... so the COEs can vary a lot. So that too can be part of the issue. Rapid cooling has NOTHING to do with the fit issue. If the glaze fits the body...... shy of raku-ing the pieces out of the kiln........ a slightly fast cooling cycle will not "cause" crazing.