RookieDev If I'm understanding what you're trying to do... I think my idea could work. This is not written in Construct 2 Event code as we're discussing logic but it's a concept made while thinking of the capabilities of the engine functions:
1) Add two objects, one of the far left of your screen and one on the far right, called LOScheckObj1 and 2. Make them transparent and with the Anchor and LineOfSight behaviours. Face the object down to the ground and give it the cone of view angle you want. Make a check on them for whatever spawn timing you're wanting (every second, two, etc.).
2) In the above condition you want to check if a floor object is within LOScheckObj's sight angle. Then, on the floor object, you'd need a condition for if in LOS of LOScheckObj, and if so, then that floor object can spawn an enemy of your choosing.