Turning the engine over with power to the ign. module and no plug installed is not a good plan. There is going to be a spark created, (as a rule) and if it can't find a place to ground where it's supposed to, it's going to go look for some place else. Unfortunately, that can often be the pickup, made with components that are not going to like that spark much at all. They're frequently blown.

That silicone insert in that plug boot is easily damaged in a rough/nose over landing, that can cause a spark leak to the metal boot jacket, even if there is no apparent damage to the boot externally. This can lead to a no start/hard start, or erratic running. Unpredictable spark would be the thought. To complicate further, a plug inserted in one of these damaged boots will often spark just fine when not installed in the head - only to break down totally when installed and under compression. Not sure if any of this applies here, but you should have the potential for this scenario in mind when things start going badly after a less than graceful landing/arrival. A lot of us flying gas frequently keep an extra ignition in stock, just cuz....

I would encourage you to remove the cowl and leave it off for the next few flights. You eliminate the potential for over heating, as well as the pressure differential thing, and the carb is MUCH easier to get to for quick adjustments. This will often let you try adjusting one way, making it better or worse, and moving on from there. Once you have it dialed in and some confidence built up, then install the cowl, knowing full well if there are problems at that point - they're cowl induced.