By `1 tbsp of x` should I assume heaped tablespoon or leveled tablespoon?
Unless the recipe specifies "heaping", read spoon measurements as level. That goes for cup measurements as well. Unless the recipe specifies another method to fill your measuring spoon or cup, use yet another implement to fill the spoon or cup, then level it by scraping with a knife. That is the most precisely repeatable way to measure (especially flour) with a cup or spoon.

The one exception to the "spooned and leveled" technique is in the measurement of brown sugar. Recipes will usually call for brown sugar to be "packed", which is just as at sounds. Press the brown sugar into the spoon or cup to squeeze in as much as you can and still have a level top.

It's far more accurate to measure by weight but most non-professional recipes in the US are written with volumetric measurements. For baking especially, consider converting volumetric measurements to weight using sources like this: Master Weight Chart, and measuring with an accurate digital scale. Depending upon the methods used in developing the recipe, measuring by weight the first time you make a recipe may not get you any closer to the measurements the author of the recipe intends, but at least your results will be accurately repeatable and tweakable.