Hi Michael, the reason we say to cover your starter "loosely" isn't because it needs airflow in order to ferment properly (it doesn't). Rather, the concern has to do with fermentation gases collecting in a tightly lidded container and causing the top to pop off. That being said, it's still important to cover the starter securely enough so that the surface doesn't dry out. A towel or cheesecloth can let in too much air and cause the top of the starter to crust over. 

I've found that as long as there is sufficient headroom above the starter level for gases to accumulate (the starter should be able to double, plus more room above that for the gases), and you open the jar now and then to vent the gases, a lid is fine. You can also just set the lid on top of the jar rather than screwing it down tightly. Covering your jar with plastic wrap is also a reasonable solution, since this will flex. In your case you might find it's helpful not to clamp down your lid tightly, unless your starter is going into the refrigerator, where I think it's important to keep it securely covered. 

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